Setting up a Backup Mail Server

Paul Howarth paul at city-fan.org
Tue Apr 19 14:04:23 UTC 2005


Reuben D. Budiardja wrote:
> Hello,
> I have my own domain, let's say: myrealname.org. I already set up a mail 
> server (mail.myrealname.org) and MX record for that domain, with MX = 10 and 
> it works just fine.
> 
> What I need help is with the following. 
> I want to setup a backup mail server with MX = 20, so in case the main mail 
> server is down, the backup mail server will collect the incoming mail. The 
> backup mail server, let's call it myothermachine.org is on another network. 
> How do I set up the backup mail server (using sendmail) to do the following
> 
> (1). If mail.myrealname.org is down, collect the incoming mail for that 
> domain, and keep trying to relay the incoming to the mail.myrealname.org.

Put myrealname.org in /etc/mail/relay-domains on the backup mail server.

> But 
> the backup mail server should _never_ inform the mail sender that 
> mail.myrealname.org (I've played around with this a bit, and by default the 
> backup mail server sends a respond back to the mail sender saying basically 
> that the main mailserver is down, and it keeps trying to relay. I don't think 
> the sender needs to know that).

Put:
define(`confTO_QUEUEWARN', `10d')dnl
in sendmail.mc on the backup server. The idea is that the queue warning 
timeout is longer than the queue return ("I've given up trying to 
deliver this message") timeout, which is 5 days by default.

> (2). While doing (1) and keep trying to relay to mail.myrealname.org, I want 
> the backup mail server to also send a copy of all incoming mails to yet 
> another account, say "myname at gmail.com". So in the case that I am away and 
> cannot bring the main mail server up, I still can get to my emails.

You're on your own there. That's both delivering and queuing mail at the 
same time. You'll probably need to script it.

 > When the
> main mail server is back, then the backup mail server should flush all the 
> mails that it stores to the main mail server.

This will happen automatically when the backup server retries delivery, 
but you can get the main server to "pull" the mail using the etrn.pl 
script, which you can find easily by googling.

Paul.




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