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
