What Emails can I send using your Smarthost?

Anything that's not spam or contains a virus.
You can put any email address you like as the From and Reply-To fields in the emails you send using our servers.

How Many Emails can I Send with your Smarthost?

We estimate that an average business user sends between 300 and 500 emails per month.
A company may send out a newsletter to, say, 1000 customers and perhaps a few people forward all their incoming email to their Blackberry.
A typical company with less than 20 employees might send out 5000 emails per month for which we charge £14.50.
If you go over the 5000 mark in some months, even by as much as 50%, we're not going to worry. There's no "hard limit" to the number of emails you can send and we'll certainly talk to you first, before taking any action, if you regularly exceed your allocation by a large amount.
For every extra block of 5000 emails you want to send, we charge £7.50 per month, up to 50,000, after which it drops to £7.50 per 10,000.

There's no real limit to the amount of emails we can send so, if you're a large company or ISP, tell us what you need.
If you're not sure how many emails you're going to send, don't worry, we'll be counting them during your free trial period, to see which price-band you fit into.

We don't charge by the size of the emails you send.
A one line email costs the same as an email with a 10mb attachment and there's no monthly limit to the total amount of bandwidth you can use to send all of your emails.

An email sent to multiple recipients splits into one email per recipient at our servers.
So, for example, an email with a total of 50 To, CC and Bcc recipients counts as you sending 50 emails.

What Size of Email Attachment can I send using your Smarthost?

We accept email attachments up to 40mb in size but this does not guarantee that the receiving server will accept attachments of this size and, in general, you'll be lucky if you can successfully send a file larger than 10mb.
We just don't want our servers to be the limiting factor.

But we have a solution to this problem:-

	You upload the file you want to send, using FTP, to a storage area on our servers which is also linked to a webserver. (Using FTP is not hard these days when you use one of the excellent free FTP clients available, such as FileZilla.)
	You then include the link to the file in the body of an email.
	The recipient clicks on the link and downloads the file in their browser.

The size of file you can send this way is only limited by the amount of server storage space you have and a 300mb file wouldn't be unreasonable to send this way.
FTP storage space is an add-on extra to our Smarthost and Ring Fence services and costs  £4.99/gigabyte/month.
There's more details of this FTP/Webserver file sending solution here.

What Types of Files can I send as Attachments?

All except those likely to contain a virus.
EXE files are the only file-type we block that's likely to cause you a problem, but the majority of email systems block these as well.
If you ever need to send an EXE file, you can send it inside a ZIP file or rename the file extension to TXT and instruct the recipient to rename it back when they've received it.
A full list of the files we block is given in the anti-virus section later on this page
If you use the FTP/Webserver alternative way of sending files, no files are blocked and this can sometimes be the only way to bypass the file restrictions of the recipient's mail-server.

To Authenticate or not to Authenticate

When you want to send an email to our Smarthosts you usually have to provide the username and password we've given you, before your email is accepted.
Many mail-servers, such as Exchange, can perform this authentication automatically but there are some situations where authentication by the sender is not possible.
If you tell us the IP address your mail-server is operating from, we can exempt this IP address from having to authenticate before sending.
The only problem with this is, if you change your IP address, you'll have to remember to let us know the new IP address in order to continue to send emails without authentication.

Using our Smarthosts to send out Newsletters and Marketing Emails

Arrowmail is about sending standard business and personal emails as reliably as possible.
We'd rather not send Marketing Emails, as it's this type of email that causes us all the problems with complaints about us sending out spam.
Saying that, we also have many customers who send Newsletter/Marketing emails through us successfully and without any problems.
The question is, do you know the ground rules for sending these types of emails?
Will you stick to them despite the temptations to market your product or organisation as widely and forcefully as possible?
Are you prepared to put in the effort to keep your mailing lists up-to-date?

If your main purpose in considering using Arrowmail's smarthost service is to send out Marketing emails then please read our rules on this page before wasting your time and ours by applying for a trial, generating complaints for sending spam, getting our servers blacklisted and having your account suspended.

Who Are Ya? Who Are Ya?

We get a lot of fraudsters applying for a free trial of our Smarthosts, hoping to use them to send out their spam so, when you apply please help us to confirm that you are genuine by:-

1 -	Using your company email address and not a free address such as Yahoo or Gmail.
2 -	Giving us the address of your company website.
3 -	There may be perfectly valid reasons why you can't do any of the above so email your request to info@arrowmail.co.uk or use the Trial Request Webform to request a phone call from us so you can explain your situation.

We value our customers and apologise for any delay or inconvenience our security checks may cause.

What Happens if Your ISP is Blocking Port 25?

To send email on the Internet you must use TCP Port 25.
Some ISPs block this port, outgoing, to prevent virus programs with built-in
mail-servers, sending out spam and other undesirable emails from an infected PC.
The only thing you're allowed to connect to, over port 25, is the ISP's own SMTP server which you are, therefore, required to use.
Using the ISPs SMTP server may be fine but sometimes, if you aren't using a From address in your outgoing emails that has been allocated to you by the ISP, these emails will be rejected by this SMTP server.
The solution is to send your emails to our Smarthost using a different TCP Port and we'll then send these emails on to their destinations using the standard port 25.
All our servers are setup to receive emails over ports 25 and 587.

There are Emails that our Smarthost Just Can't Deliver

 

"It's my job to monitor the mail queues on Arrowmail's Smarthost Servers to check that things are running smoothly, and the queues I'm particularly interested in are the Outgoing Queue, the Retry Queue and the Bad Queue. The vast majority of emails zip in and out of the Outgoing Queue in a fraction of a second, on the way to their destination. If the first attempt to send an email fails then this email stays in the Outgoing Queue for an hour and, every minute, another attempt is made to send the email to each of the servers listed in the destination's MX records, in turn and in order of priority. An attempt is even made to send to the default IP address of the recipient's domain as the RFC documents that specify how email should work, don't actually require the use of MX records. Emails often hang around in the Outgoing Queue for 10 minutes or so because the receiving mail-server is playing the "grey-listing" game: purposely refusing an email for a set period of time to test the persistence of the sending server, with the assumption that mail-servers sending millions of spam emails won't be very persistent. You've never seen servers as persistent as our Smarthosts! Other emails don't get delivered because there are no DNS records containing instructions on where to deliver them, or the mail-servers that are specified aren't responding. There are 4 main reasons of this:- 1 - The To: email address is spelt incorrectly. An email to johnsmith28@hotmail.comn is never going to be delivered because the top-level domain is invalid, but Outlook doesn't complain about this when you click Send. 2 - The email trying to be delivered is an automated reply to some spam that's been received from a made-up email address. This could be an Out-of-Office reply, a polite message saying that the email to adolphyang@yourcompany.co.uk, or some equally unlikely sounding member of staff you've never had, couldn't be delivered, or even a message from your server saying:- "Your last email was rejected as spam". Please, all you Exchange Administrators out there, these messages, provoked by a spam email, are just as much a waste of Internet bandwidth as the spam itself, so stop your server generating them! Instructions on how to stop Exchange doing this are here. Or perhaps you just need a better anti-spam system, like the one found elsewhere on this page. 3 - The To: email address, or even the whole domain itself, was once valid but has now lapsed and the person or company you're trying to contact has either got a new email address or ceased to exist. 4 - The recipient's mail-server is having temporary technical problems or perhaps the MX records are in the process of being changed. When an email still can't be delivered after an hour, 2 things happen:- 1 - The email moves to the Retry Queue. 2 - A warning email is generated and sent back to the sender which says:-   ------------------------------------------------------------------------------------------------------------------------ Email Delivery Status Notification from mailout1.arrowmail.co.uk ------------------------------------------------------------------------------------------------------------------------ We've been trying to send the attached email message every minute for the last hour without success. The email has now been moved to the Retry Queue where further attempts to send it will be made once an hour for the next 3 days. If the message can't be delivered after 3 days you will be sent another notification email. Only a small percentage of emails in the Retry Queue ever get delivered and this is usually because the recipient's email address is invalid, either it's spelt wrongly or is no longer current. Please check this now and, if you find an error, send a new email with the correct address information. ------------------------------------------------------------------------------------------------------------------------ THIS IS A WARNING MESSAGE ONLY - DON'T RESEND THE ORIGINAL EMAIL ------------------------------------------------------------------------------------------------------------------------ This warning email also contains an extract of the conversation between our Smarthost and the receiving mail-server which often reveals the nature of the problem: non-existent user, mailbox full, etc. This warning email is sent because you need to know if your email hasn't been delivered after and hour and, most-times, you'll spot the spelling mistake that you made in the To: or CC: address straight away, correct it and re-send the email. An attempt to deliver emails waiting in the Retry Queue is made once every hour for three days. This gives time for any failed server to be repaired or changed MX records to propagate around the Internet. To be honest, only a very small percentage of emails, usually those destined for servers that manage to recover from their technical difficulties, ever get off the "Death Row" of the Retry Queue, and that's despite all the conscientious efforts of our Smarthosts. The Retry Queue is a great indicator, for me, as to when there are problems I need to investigate. For example, if the Retry Queue suddenly has 200 emails waiting to go to yahoo.com addresses, I have to activate a routing rule to send emails, destined for Yahoo, via a one of our alternative mail-servers while I approach Yahoo to see what they think we've done wrong. After 3 days is up, emails from the Retry Queue move to the Bad Queue and the sender receives this obituary:-   ------------------------------------------------------------------------------------------------------------------------ Email Delivery Status Notification from mailout1.arrowmail.co.uk ------------------------------------------------------------------------------------------------------------------------ The attached email could not be delivered and has now been deleted from our servers. Either the recipient's mail-server refused to accept the email or the email has been in our Retry Queue, trying to be delivered for the last 3 days without success. ------------------------------------------------------------------------------------------------------------------------ YOUR MESSAGE WAS NOT DELIVERED TO ONE OR MORE RECIPIENTS ------------------------------------------------------------------------------------------------------------------------ Sometimes you'll receive the above message just minutes after sending an email if the receiving server flatly refuses to accept the email. When a server refuses an email with an error-code in the 500s, RFC-compliance means we mustn't attempt to send that email again. Emails in the Bad Queue are periodically deleted. It's worth mentioning that if you send an email to multiple recipients, including copies (CCs) or blind copies (BCCs), your email splits into one email per recipient when it arrives at our Smarthosts and each email is then treated separately, so one bad address won't prevent your email being delivered to all the other recipients.

Add a "Footer" to all your Outgoing Emails

If you want, our servers can add a message to the bottom of each email that you send out.
An example might be something to convince the recipient that you emails aren't spam:-

Scanned for viruses by Arrowmail using Kaspersky Labs.
Sent from a Sender Policy Framework specified server.
DomainKeys Identified Mail digitally signed by arrowmail.co.uk

There's no extra charge for this and your own mail-server may be able to do this more conveniently but, if this can help, we're happy to enable it for you.

Encrypting Outgoing Emails

Our Smarthost supports (but doesn't require) TLS encryption (Transport Layer Security) when receiving emails from your server.
Using TLS means your emails will be strongly encrypted as far as our servers.
To enable this on your Exchange Server is simply a tick in a box (exactly where to find this tick-box is shown on our Smarthost configuration instructions page here).

Whether or not you use encryption to send emails to us, our Smarthosts will attempt to negotiate an encrypted channel when sending your emails onto the receiving mail-server but, in most cases, this is declined by the other mail-server and the emails pass in plain text.
Our Smarthosts do their best to keep your outgoing emails encrypted but can't guarantee they'll remain encrypted all the way from your Outbox to the recipient's Inbox.

Create a Special DNS Record to Help us Send your Emails More Reliably

If you decide to use our Smarthost servers, you can help lessen the chances of your emails being classified as spam by creating a special DNS record called an SPF record

This DNS record is to comply with the Sender Policy Framework (SPF) anti-spam initiative and it identifies our servers as being approved for sending emails from your domain.

For more details about how to create an SPF record, click here.

We also attach a DKIM signature to each outgoing email to comply with another anti-spam initiative.

Our Ring Fence service requires no equipment or software to be installed on your server or your LAN.

These 2 steps are required to set it up:-

1 -	Edit the DNS MX records for your email domain. You need to set our mail-servers to be the ones responsible for all emails sent to your domain. You do this by editing the DNS MX records for your domain as shown below:-
	We're happy to edit your DNS settings for you if you can let us know your domain registrar control-panel logon details. After changing your MX records, all incoming emails sent to your domain will now come to our servers. This has the added bonus of reducing the amount of Internet bandwidth and server resources you're wasting on dealing with spam.
2 -	Configure your mail-server to use our servers to send all your outgoing email. If your mail-server is Microsoft Exchange, there are instructions for configuring it to send all outgoing email using our servers here. We're happy to perform these configuration steps for you if you're prepared to give us remote access to your server.

Lost Email Protection

If your server or Internet connection fails, we'll hold all your incoming email on our servers, indefinitely, until your server comes back on line when they'll then be automatically forwarded on.
While your server is off-line we can send a copy of all incoming emails to an external address, such a Gmail, so you can continue read incoming emails.
You can have up to 4 email domains covered by Lost Email Protection in our Ring Fence package.

More Information

Anti-Virus

We scan all attachments in your emails for viruses and delete them if any are found.
Attachments of types used almost exclusively for sending viruses are also removed.

More Information

Spam Filtering

We classify all your incoming emails into:-

Not Spam	These are passed, unchanged onto your server.
Definite Spam	These are deleted.
Probable Spam	These have their Subject Line modified to add the Spam Score so that you can use Outlook Mailbox Rules to automatically move these emails, as they come in, to your Junk E-mail folder where you can check them, occasionally, for False Positives. Optionally, we can send all Probable Spam to a single separate mailbox on your server so that one person at your organisation can check for False Positives for all of your users.

Spam that our servers have missed, or any False Positives you find, can be re-submitted to our Spam Filtering system. Instructions on how to do this are here.
Phishing and Backscatter emails are also trapped by our Spam Filter.

More Information

Smarthost

All your outgoing emails are sent from your server to our SMTP servers which then deliver them to their final destinations.
Sending emails used to be a simple process but, with all the anti-spam measures now in place across the Internet, it requires special techniques and configuration settings to maintain a
mail-server's status of being trusted by other mail-servers as a source of genuine emails.

More Information

WebSend

If your email system is down, this webpage allows you to send out an email which will appear to have come from your usual company email address.

Another use is if you want to send an email using a different company email address as the From address, such as info@, but your Outlook isn't setup to do this.
Have a look at this page here

Server Alerts

If you administer your company's email server you'll know that there are things, beyond your control, that can cause it to stop working: services can stop, the Internet can drop out, a power failure can make the server or router lock up, …and the list goes on.

You probably know how to fix most of these things, but the trick is to know when something has happened and take the necessary action before everyone starts ringing you to say their email isn't working.
We offer an alerting service that will email you and then send a text message to your mobile phone when your server has stopped responding.

How does it work?

Every 15 minutes, our servers try to connect to your server over TCP port 25 - it can be a different port if you prefer. If your server doesn't respond we send you a warning email which would be to an alternative email address, not hosted on your server, such as Gmail.
If your server doesn't respond at the next monitoring interval we send a text message to your mobile phone.
When your server does eventually respond again we send you another email to say that it's working again.
The text message would therefore be sent between 15 and 30 minutes after your server has failed.

Some points to note:-

	Text messaging is only available to UK phone numbers.
	This service does not require anything to be installed on your server.
	Your Internet connection needs to have a static IP address or use a Dynamic IP tracking service and at least one incoming port needs to be open on your router.
	Just because your server responds to a connection attempt from our servers doesn't guarantee that your Exchange server is fully-functional as some important service could still have failed. If you can allocate a mailbox to us which has POP3 access from the Internet, we can perform a more rigorous check by sending an email by SMTP and then attempting to collect it again using POP3 and generating alerts if the collection process fails.

Dynamic IP Address Tracking

A static IP address can cost an additional £5/month from your ISP, or maybe your preferred ISP doesn't offer the option of a static IP address.
When you subscribe to our Ring Fence service we include the option to allocate you a DNS name such as mycompany.arrowmax.co.uk.
You then install an Update Client on your server which monitors your IP address and, whenever it changes, it contacts our DNS severs to update your DNS name with the new IP address.
This means that you can operate your mail-server from behind a dynamic IP address without any problems.
Your server can also be accessed by your users for Outlook Web Access, Remote Desktop, VPN connections, etc. using the same DNS name.

If your company runs its own email system using a server located at your main office then you're likely to have only a single MX record, such as shown below:-

If this server becomes unavailable there's nowhere for your emails to be delivered!

You can add our 3 servers as lower priority MX records, as shown below:-

When a mail-server is delivering an email, it first tries to send it to the nominated receiving server with the highest priority and, if this fails, tries the server with the next-highest priority and so on.
Priority, or preference, is a number between 0 and 99 and the lower the number, the higher the priority.
It would be extremely unlikely that all 4 servers, in the above example, are unavailable at the same time.

With your MX records setup as above, if your server or Internet connection ever has a problem, our servers will be receiving your emails and attempting to forward them on to your server every 15 minutes, indefinitely, until your server comes back on-line.

We can also send a copy of all the emails waiting on our backup servers to an external email address that you nominate, such as a Gmail address, where you can then read the emails that have been sent to you while your server's down.
When your server comes back on-line, all the originals of these emails will still be delivered to your users' mailboxes.
The only catch with this is that, in the external mailbox, all your company's emails are lumped together so, whoever is checking it, can read everyone's emails. You'll therefore have to decide if you want this feature and who it's appropriate to allow to access this external mailbox.
You also have access to our WebSend webpage which allows you send emails that appear to originate from your normal company email address. Have a look at this page here.
With forwarding to an external address and the WebSend page you can almost operate as normal when your email system has failed.

When your server is operating normally, the occasional email will get sent to our backup servers. These will be immediately sent on to your server without generating a copy to the external address.

We're happy to create the appropriate MX records for you if you can give us access to your DNS control panel.

Check out our Rolling Archive service, which holds a copy of all your company's email for the last month, in case some disaster with your server causes you to lose the originals.

This does mean the odd spam message will make it into your Inbox (some days are worse than others) but, more importantly, some genuine emails will need rescuing from your Junk folder, a job only a human can do.

To take advantage of our anti-spam system you'll need to modify the MX records for your email domain so that all incoming emails are routed via our servers before being send on to your server.
Your MX records should be set as shown below, substituting your email domain for mycompany.com

There's more information on MX records here.
We're happy to create the appropriate MX records for you if you can give us access to your DNS control panel.

Classifying Emails into Various Categories

We then classify all incoming emails into 3 categories:-

Not Spam	These are passed on, unchanged, to your server.
Definite Spam	These are deleted.
Probable Spam	These have their Subject Lines modified to add the Spam Score, as shown below, so that you can use Outlook Mailbox Rules to automatically move these emails, as they come in, to your Junk E-mail folder which you can then check, occasionally, for False Positives. 3 examples of modified Subject Lines are shown below:-
	The characters your rule should look for in the Subject Line are:- [***SPAM*** Score/Req: Optionally, we can send all Probable Spam to a single, separate mailbox, on your server or ours, where one person at your organisation can check for False Positives for all your users.

If you take the option for all your company's Probable Spam to go into one mailbox on our servers, each email stays there for 7 days before being automatically deleted.
This gives a chance for someone in your company - the Spam Meister - to use, most likely, Outlook Express and an IMAP account to check the Spam folder for false positives - doing this once a day is usually sufficient.

If you find false positives from regular correspondents then you can send us their email addresses for white-listing.

You can forward any spam that makes it into your user's Inboxes, as well as any False Positives you find, back to us, so our spam filtering system can learn from it's mistakes.
They have to be forwarded in a special way in order to preserve their original formatting, details are here.

Refusing to Accept Emails from Blacklisted Servers

95% of spam never makes it to our Spam Filtering system because the servers trying to send them to us are on a blacklist and so we simply refuse to accept emails from them.
Our servers actually tell the sending server there's "No such user here" which is the best strategy to stop the server trying to resend the spam.

The organisations that run these mail-server blacklisting services are very good at it: a new rogue server can be listed within an hour, and a genuine server that has been compromised but has now recovered can also be de-listed within an hour.
Mail-servers aren't blacklisted by the country they're in, because they have a dynamic IP address or an incorrect, or missing, Reverse DNS record, but simply by being identified as having sent out spam and so this doesn't lead to genuine emails being falsely identified as spam.

If your company is drowning in spam, or you current anti-spam measures aren't working then give our system a try

These are the advantages:-

1 -	A dramatic reduction in the amount of spam arriving in users' Inboxes - but not quite a total elimination yet.
2 -	A system where you can easily identify and recover false positives.
3 -	There's no need to subject new senders to an authentication process before their email will be delivered.
4 -	The hordes of spammers will no longer be banging on your door, wasting your firewall and server resources plus chewing up your Internet bandwidth. The changed MX records will have sent them all away to our servers to be dealt with.
5 -	Because of the way our anti-spam system works, you automatically get Lost Email Protection included, detailed elsewhere on this page.

Our spam filter is very fast so the delay in routing emails via our servers and then onto yours, instead of your server accepting emails directly is usually no more than 1 minute.

FTP has a reputation as being "geeky" and insecure.
Modern graphical FTP clients hide all the underlying geekiness and Arrowmail supports secure FTP, where all file transfers and the exchange of passwords are performed using strong encryption.

All operating systems follow the same FTP standards so the computer used to upload or download a file can be a Windows PC, a Mac, a Linux box or just about anything else.

Here are some quick definitions of FTP jargon:-

FTP Client	The program you run on your PC to access an FTP Server to upload or download files.
FTP Server	The program that runs on a server computer, connected to the Internet, which stores the files that have been uploaded and makes then available for downloading.
Resume	If you are downloading a 300mb file from an FTP server and your Internet connection fails after 290mb have been downloaded, the ability to "resume" means that, once you've reconnected to the FTP server, you can pick up where you left off and just download the last 10mb of the file instead of having to start from the beginning again.

There are many, very good FTP clients available.
We recommend the free one called FileZilla

To access an FTP Server you only need 3 bits of information:-

1 -	The Hostname of the FTP Server - such as ftp.arrowmail.co.uk
2 -	Your Username for the server
3 -	Your Password for the server

When you connect to an FTP server with FileZilla, the left-hand window shows files and folders on your local PC and the right-hand window shows files and folders on the FTP server.
Drag-and-drop left-to-right to upload, right-to-left to download.
How hard is that?

There's more info about using an FTP client here.

OK, so you might be able to work out how to use an FTP Client to upload files, but are your customers going to find using FTP so easy? Don't answer that because they don't have to!
There's also a webserver running at the location where your FTP files are stored, so files can be downloaded using a web browser, which is another thing that everyone, including your customers, knows how to do.

As an example, if you upload a file called brochure.pdf to the Arrowmail FTP server, you can send your customers an email containing the following link:-

https://www.arrowmail.co.uk/yourcompany/public/brochure.pdf

and when they click on the link in the email, the file called brochure.pdf will start to download - give it a try!
(Note the https:// prefix, signifying that the file will be downloaded over a strongly encrypted channel - http:// also works.)

How cool is that? It makes your company look like it knows a thing or two about the Internet.

Files in the /public/ folder can be downloaded by anyone as long as they know the name of the file, but they can't change or delete files, upload new files or browse the Public folder for any other file that takes their fancy.

If you had uploaded brochure.pdf to the /yourcompany/ folder and emailed the link:-

https://www.arrowmail.co.uk/yourcompany/brochure.pdf

then the browser would ask for your username and password before it would allow the file to be downloaded.

Arrowmail's FTP/Web Server combination allows files to be easily and conveniently sent to customers as well as allowing confidential files to be transferred securely to people that you trust.

When an infected email is found it's simply deleted.
No email with a virus attached will have any legitimate content.
We don't send an NDR (Non-Delivery Report) or other notification to the sender or recipient.
The sender's address will have been forged, you don't need to know about yet another attempt to send you a virus email and so we don't want to waste any more Internet bandwidth for the sake of a virus.

As a second line of defence, we also perform "Pre-emptive Virus Protection".
This means deleting emails with file attachments of the types used, almost exclusively, for transmitting viruses.
In this way we provide protection against new viruses which our virus scanner doesn't yet know about.

These are the attachments types that we currently block:-

ade

adp

bas

bat

chm

cmd

com

cpl

crt

exe

hlp

hta

inf

ins

isp

js

jse

lnk

mbd

mde

msc

msi

msp

mst

pcd

pif

reg

scr

sct

shs

shb

vb

vbs

vbe

wsf

wsh

wsc

The file-types filtered out by our email servers could, if double-clicked on, cause Windows to open the file in a program that will then automatically execute code to install a virus or perform some other undesirable action.

All other file types, including DOC, DOCX, XLS, XLSX and PDF files, are only deleted if they are determined to be carrying a virus.

Microsoft Office files are not so safe, and they have been known to carry macros that act like viruses. However, if they get the all-clear from our virus scanner, we let them pass as it wouldn't be practical to block such popular files on the basis that they may contain an, as yet unknown, macro virus.

It is highly unlikely that you would ever want to send or receive files of the types blocked by our mail-servers.
EXE and MSI files may be used legitimately to send software installation programs but it is too risky to allow them to pass.
If you do want to send someone an EXE file we advise that you put the EXE file inside a ZIP file and attach the ZIP file or you could change the file extension name to TXT before you attach it and let the recipient know to rename it back to EXE after they've received it.

Although there are many examples of ZIP file email attachments containing viruses, we do allow them to pass if a scan of the ZIP file's contents doesn't show any viruses

Remember that all commonly used file extensions are allowed to pass via our mail-servers after virus scanning. This includes DOC, DOCX, XLS, XLSX, PPT, PPTX and PDF.

We include virus-scanning as a free extra to all the services that involve your emails passing in and out of our servers.

Finding viruses in emails is relatively easy and reliable compared to determining which emails are spam.
There are, however, many emails around that do not contain viruses and are written in simple, plain non-spammy language which, however, contain a link to a webpage which will try and trick you into downloading a virus, spyware program or revealing personal information.
Some of these email will be caught by our spam filter but others will get past our filters and so you still need to employ the following protective measures on your PC to be completely safe:-

1 -	Real-time Antivirus Protection
2 -	Anti-Spyware protection
3 -	Common sense

And, by the way, we will never send you emails saying that unless you click on a link and update your details we will suspend your account.
In fact you should treat any email, claiming to be from us, that you weren't expecting, as suspicious.