Published Wed, 04 Jun 2008 15:11:00 +0000
Next week we'll be installing a new 'tertiary-mx.co.uk' server to
replace the current one. The new server operates slightly differently
to the old server as it will be doing more spam checking. We are also
looking to add access to logs of this server for customers in the near
future too. Here are some details of the new mail server: (If you have
any questions please do email support)

"tertiary-mx.co.uk", located in Maidenhead, can be used as a backup
email relay - typically for customers running their own email servers
on their ADSL lines. The server will relay email for any domain on our
system that has the email service selected, as well as sub-domains of
that domain. (Email service is £1/month +VAT per domain as usual, which
includes sub-domains)


 A backup email server is a prime target for spammers, as often the
backup email server does less spam checking than the primary server. To
combat against spammers Tertiary-mx.co.uk does do some spam checking
and will reject or defer connections/messages in some cases. The idea
here is for tertiary-mx.co.uk to permanently reject messages that are
obvious malware or spam based, and to defer 'dodgy-looking' messages so
that the sender needs to retry and use the primary mail server, which
will then decide what to do with the message.


Reject:
Rejecting means the message is not accepted and a permanent error
message is given, meaning the sending server will bounce the message
back to the sender. They won't try sending it again to us or any of the
other mail servers listed for the domain.
We do this if:

the sending server gives an invalid EHLO/HELO (The HELO needs to be a
fully qualified domain name) the sending server doesn't stick to proper
SMTP protocols the sender email address is invalidthe message contains
a virus the message has a spam score of over 20 (normally over 5 points
is a spam message)  Defer:
Deferring means that the message won't be accepted and a temporary
error message is given. The sending server will have to retry at a
later time, and when it retires it should then try the primary server
anyway.
We do this if:
the sending server doesn't have a reverse DNS entry the sending server
is in a DNS Blacklist. (It checks a few blacklists) the sender address
is invalidthe recipient address is invalid (It'll attempt a 'callout'
to check it)the headers fail a syntax checkthe message has a spam score
of over 7 points. (normally over 5 points is a spam message)Other
Notes:
When it accept a message a header line with the spam score we gave it
will be added.You can use 'etrn' to request messages for your domain to
be retried: telnet to tertiary-mx.co.uk on port 25, and type: etrn
your.domain.name  tertiary-mx.co.uk will keep trying to relay email to
a lower MX for a period 21 days before bouncing the message back to the
sender. There is not a way to collect email by POP3 or IMAP from
tertiary-mx.co.uk, but we hope to be able to offer logs showing details
of held mail in the near future.Customers can use our 'C' email server
as a backup email as an alternative to tertiary-mx.co.uk. The C server
will store email it accepts which can be collected by POP3 or IMAP, it
won't attempt to relay email to a lower MX. For more information on
this please contact Support.Customers using the old A/B email servers
as a backup relay should move to tertiary-mx.co.uk instead, again,
please contact support for advice with this.

See http://aaisp.blogspot.com/2008/06/details-of-new-tertiary-mxcouk-email.html