>I'd like to get some ideas/thoughts from the group on how to setup a backup
>mail server plan.
There are three methods you can use:
[1] MX records: This was designed for redundancy, and is easy to implement.
[2] Other DNS tricks: This, too, was designed for redundancy (IE multiple A
records).
[3] Clustering: This is very difficult.
>My questions are this:
>
>1) Does anyone have a system setup and working like this? If so, some
>general configuration notes would be nice.
Lots of people have a backup MX record, that points to a mail server that
will accept E-mail and keep re-trying to deliver it until the main server
is back online.
>2) If Box 1 goes down, what's the best way to switch to backup box 2 (MX
>records?)
Yes. MX records were designed for this purpose.
>3) What about the mailboxes on box 1 if it crashes? Are they gone?
Yes. Unless you use clustering, there's no way to access those mailboxes
until they can be restored from a backup.
>4) Do I need to maintain duplicate user accounts on both boxes?
No (the backup will accept all mail for @example.com, and forward it to the
primary mail server, which will accept it or bounce it if it will not
accept mail for the user).
If you use clustering, you may have duplicate user accounts, but you may
not even know whether or not you do.
>5) If box 1 goes down for a bit... and I switch to box 2.... then get box 1
>back up and running. Can I get email that is sitting on box 2 over to box
>1? Easily? :-)
It will normally take 20-30 minutes (depending on how often the backup mail
server retries delivery), but can normally be sped up by sending an ETRN
command (I don't think IMail will send it, as it may not know that it was
down, but you can send it manually).
So a backup MX record would be relatively easy to implement, but won't
allow you to access mail (POP3, IMAP, web messaging) until the primary is
back online.
To be able to access mail while the primary is down will be a very large
undertaking involving clustering. Some mention has been made here about
clustering, and a few people have done it, but it would likely be difficult
to set up.
-Scott
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