Tertiary-mx

tertiary-mx.co.uk is our backup email server. It will accept email for a domain we handle email for and will queue messages and will attempt to deliver to the higher priority MX record.

Spam Protection

Tertiary-mx.co.uk does do spam checking and will defer email that looks like it is spam in some way. It will deny (cause a permanent delivery failure) messages/connections under the following circumstances:

• Invalid HELO
• Recipient domain is not one we handle email for
• Message size is over 1Gb.
• The server will 'greylist' hosts. It will always defer (cause a temporary delivery failure) messages/connections under the following circumstances:
• Sending host in a DNS blacklist
• Header syntax errors
• Recipient rejected by the primary MX (It does a call back to the primary MX if it is available)
• Senders email address can't be verified
• Contains malware (including spam/phish signatures) as picked up by the virus scanner
• If the SpamAssassin spam score is over 6

The reason for deferring is so the sender is forced to use a higher MX, where it can then make the decision whether to accept or deny the message. -This gives customers running their own servers more control over spam.

Queuing

Messages will be attempted to be sent on to a higher priority (i.e. lower MX record) email server starting at every 15 minutes, and increasing over time to every 3 hours. It will carry on trying for 31 days before bouncing the message back to the sender.

Setup

If you would like to use tertiary-mx.co.uk as a backup mail server for your domain please contact sales who will add the domain.

If you manage your own DNS server, then you'll want to add an entry similar to:

example.com   MX   50   tertiary-mx.co.uk.