It is possible? Emails - backups.

[Carstea Catalin]

How can i configure 2 server of mail :
1. One to serve my users on LAN (pop3 , smtp);
2. the second serverer is "the backup of mail boxes of first server" and 
more: 
 -> if first server is down this server gets emails for my lan users? 
  Ex: [internet]------------->[first mail server]<----->[second mail server 
- with same mailboxes as first]--------------------->[LAN]
 3. I want to run postfix.
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It is possible?
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tks!

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Carstea Catalin