Scott Silva wrote:
2) i would like to also know about MX records
i mean DNS server having MX with same priority n MX with different priority
i right now have a primary n secondary mail server that is dns server with
different MX records and its workin fine
if i have 2 servers with same MX priority do i need to create the same
users on both my centos servers so tht if one server fails othe one is
operational . i do presume the above is correct or is there any other way
You usually have your backup MX just hold the mail and forward it to the
primary when it comes back up. To have a second server become operational if
the first fails is not just about backups, it is about HA (high availability).
There is more info on HA on the Linux HA website
http://www.linux-ha.org/
There's a nice milter for sendmail called milter-ahead. This works great
on a backup mailserver as it will look 'ahead' to the primary and if it
is up, it will not accept the email. This might sound silly at first,
but if you don't do it this way, you'll find a huge queue of spam to
nonexistant users on the backup server which can't be returned to the
bad addresses spammers use... or you wind up bouncing spam to those that
did not send it... a horrid situation.
I'm not understanding your using the same MX priority settings, as there
is not really a default server. Mail winds up split between both places
instead of hitting the primary first. Spammers however will find your
backup server and send directly to it, in order to try to circumvent
rejects from the primary and create bounces out of the secondary. This
situation is almost as bad as having an open relay. You can land
yourself on a lot of blacklists quickly and become a part of the spam
problem easily.
If you do wish to have two equally accessible mailservers, users will
need to be replicated. Clustering or something like Xen could be a
better option.
Best,
John Hinton
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