Please see the following for a new mail server setup.

 

              <Internet>

                      |

              <Firewall>

                 /       \

          <mail1>  <mail2>

                \           /

                 \         /

           <POP Server>

 

The mail would come in to the mail servers, 1 and 2, (load balancing happens at the firewall).

These servers would filter the mails and drop them in the "/var/spool/mail" folders on themselves, (this is required for mail filtering).

If the mail is forwarded, it is not filtered.

The pop server needs to retrieve the mails from both servers, and allow for the end users to get the mail from the server.

This retrieval from mail1 and mail2 needs to happen every 5 minutes or less as to prevent unnecessary delays in local mail delivery.

 

Another option, or alternative is that we can "map" the "/var/spool/mail/" directory on the POP server from mail1 and mail2.

This would make the mail delivery almost instantaneous for the local users, and the mail server/filtering would be load balanced between two different servers.

The major drawback on this type of setup is that if the POP server goes offline, the mail servers cannot drop mails into it. It will then drop the mails locally. Once the connection comes back, the local directory will no longer be visible, and mails will have been "Lost", (they can be retrieved, but it takes some effort).

 

Please let me know your thoughts on this and correct me if I am wrong.

TIA,

Srujan

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