Dual MTA with Qmail

Recently i installed two qmails in a single server to handle mails from inner and outer domains. I will be posting a step by step tutorial of the same in the coming days.

Why dual MTA?

Basically i wanted two different queues to handle mails in different ways.
Queue 1) To get the mails(incoming) and pass it on to queue 2.
Queue 2) Will receive mails only from queue 1, runs virus scan, spamassassin and delivers mails to local or remote mail boxes(outgoing).

While i could have achieved the same functionality with single queue i doubted it may not suit my needs in the future. Say if the server can handle 250 mails and the queue is already full then we may see some delay in receiving mails from remote machines and/or may completely loose some mails. More over I don't have to change the incoming queue's setup and continue receiving mails until i needed. It provides me the flexibility to pass the message to different server/s altogether whenever needed.

How the setup will look like?

Queue 1: Two qmail-smtpd instances one listening on port 25 and the other listening on port 465(SSL).
port 25 - To receive mails from public domains such as yahoo/google.
port 465 - For internal users to send mails(auth + encryption).

Queue 2: qmail-smtpd listens on port 2000. Receives mail only from localhost(127.0.0.1). Calls qmailscanner and have it scanned with clamav & spamassassin. If it has virus the mail is quarantined. If tagged SPAM then the mail's subject is prepend with [SPAM] and delivered to user's mail box. If the user is local, the mail will be delivered to Junk directory.

Also there were some specific needs for me. We had many aliases in the server and only certain people must be able to send mail to those aliases. While this can be done with mailing list software like ezmlm i thought of discovering more. When a unauthorized user sends a mail to particular alias it will send a mail to the moderator. I wanted the mail to be bounced back to the sender(ezmlm has that option) and also give my own message for the bounce(reason). I wrote my own perl script to achieve this and it was simple enough. Ezmlm is also installed in my server and serving other purposes.

Enough for tonight. I will be posting a step-by-step guide in couple of days.