MX priority configuration when using a virus scanning machine in conjunction with your MTA.

[Mathias Körber]

> Are you saying that if I have a mail server with an MX priority 
> of 04 and a
> backup mail server with an MX priority of 10, and the priority 04 server
> goes down, that the priority 10 mail server will not deliver the email? It
> will just hold it until the priority 04 mail server comes back up?

That really is a decision outside the DNS. The priority field in the MX
records only specifies in which sequence the mailservers for a domain get
tried for delivery of the mail.
WHether those mailservers then attempt further delivery inside the domain
(by means of private routing information or via a separateprotcol etc)
or just hold the mail until the lowest prio (or 'a lower-prio') mailserver is
up again, and then forward it to that server is up to the admins to decide.
Both methods work (I'm sure there are more waysto do this) depending
on the mailserver setup.

Usually, in the absence of other configuration or further mail-routing instructions, 
they will just wait to deliver the mail to any of the mailservers with a lower priority.

Such further routing instruction could be
	- a different set of MX records found using the 'inside' DNS view (in a split
		DNS scenario)
	- a mailertable setup in sendmail (which overrides DNS)
	- a configuration that drops the received mail into a different
		protocol (eg an MS exchange network)
	- it could print out the mail to have it hand-delivered or somesuch
	- many other things

The MX records only specify where an outside mailserver drops mail for a
domain. WHat actually happens inside is totaly separate and differs
according to what the admins for that domain set up.

HTH HAND