2 questions about relay mail servers and secondary mail servers.

[Felix Schwarz]

Dan McCullough schrieb:
(Backup MX)
> Are there steps out there to follow?
> Are there pro's and con's?
> Any real experiences?

First of all, you should not need a backup mx as every well-behaving smtp server 
should retry after some hours. AFAIK the RFCs mention a time span of several 
DAYS. You should be able to fix a broken system in that time. Normally, you will 
mostly loose some spam...

Second, your backup mx will get hammered by the spammers as these backup systems 
  often don't have a list of valid users so they accept all localparts for given 
domains. You should make sure that you have that list.

Alternatively you could set up an ACL (exim speak, I think postfix calls that 
"Recipient Address Verification") with does a callout to your main mail server. 
With Exim you can specifiy that it should accept any local part if the main mail 
server does not answer so you will have a recipient verification at least while 
your main server is up. There should be a method to do that with postfix, too.

> So my thinking was give them a relay mail server
> that would send mail here, if it dropped it would continue retrying
> until successful, unless I am missing the point. 

I think this is correct.

> However I have been
> told that mail relay might be a problem with DSL connections as those
> typically get labeled as spam since they are dynamic IP addresses,
> technically our IP addresses are labeled dynamic even though their ISP
> consider them static.

If your main mail server has a static ip this should not be a problem as the 
receiving mail server should check only the last hop - else you would have 
trouble sending any mail at all (e.g. dialup home computer with dynamic ip -> 
your mail server -> remote mail server). And of course, you should configure 
your main server so that mail from your satellite systems is handled the same 
way as other internal mail.

fs