Setting up a Backup Mail Server

[Reuben D. Budiardja]

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. 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).

(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. 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.

Any help / pointer on how do this ? 

Thank you in advance.
RDB
-- 
Reuben D. Budiardja
Dept. Physics and Astronomy
University of Tennessee, Knoxville, TN

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