Migrate from Imail 11.03 to Postfix

What type of client access will you be configuring (IMAP/POP/Web)?  What are you looking to achieve by migrating to PostFix?

Hello Bud. We will be configuring POP. We manage email domains for several clients... Spammers have been using us as a relay to send massive amounts of spam. We've configured Imail to deliver mail only to our managed domains; but, spam continues to be relayed to external accounts. We've done everything possible in Imail to block this spammer to no avail. We are hoping postfix may improve security.

It sounds like one of your client's e-mail accounts is compromised; unless you force a password change during the switch to PostFix, you won't solve the spam problem.  iMail used to have excellent logging of authenicated SMTP sessions -- I suspect the answer is there.

Hi Bud. The spam is coming from @aol and @gmail accounts... Not a client account.

@aol and @gmail may reflect the address in the body of the e-mail, but when the spammer connects to your server, they have to authenticate with an e-maill address for one of the users you support.  This authentication e-mail does NOT have to be a domain match for e-mail being sent.

For example, if I administered the server for 'acme.com', I could send e-mail that looks like it is from 'fred@bedrock.com', but to do so I have to authenticate to the server as 'roadrunner@acme.com'.  Since I authenticated as an 'acme.com' address, the server will allow the relay of the message.

Thanks greatly for your help Bud. I'm still not sure this is the case though. Because, wouldn't we see them logging in in the Imail log file? We don't see anyone from any of our accounts making that connection.

I haven't used iMail a couple years now, so my memory may be fuzzy, but I seem to recall that you may have to configure what entries iMail should make in the log.  Specifically, you would want to log SMTP Authentication.  

Of course, I'm making the presumption that your SMTP relay option is set to "Only allow relay for authenticated users" or similar

I looked here: http://docs.ipswitch.com/_Messaging/IMailServer/v11/GettingStarted/index.htm

searched for "relay" and found this excerpt:

For secure data communication, SMTP Authentication lets you verify each user who attempts to send mail through your mail server, as long as SMTP Authentication is enabled on the IMail Server. Users need to set their mail clients to do an SMTP login; for example, in Microsoft Outlook on the Tools > Accounts > Mail > Properties > Servers tab select the option My outgoing mail server requires authentication.

SMTP Authentication is used in the following cases:

If you use the No mail relay option for SMTP relay.
If you use the Relay mail for (Addresses) option, SMTP Authentication enables users who send from IP addresses that you do not list; for example, users who are traveling and do not have a static IP address.

I greatly appreciate your help Bud. Still, I need advice on migrating from imail 11.03 to postfix. What the best way to achieve this with minimal user interruption?

We've kinda circled back to my original post -- what will you be installing beside PostFix to handle the clients?  PostFix is a message transfer agent (MTA).  It knows how to deliver messages from one mail server to another, and how to accept messages for a domain and store them in a mailbox.  The installations I've seen then have some other software to handle client communication (via IMAP or POP) with the mail box; PostFix does not do that.

Bud, I want to thank you again for your assistance. Here is our planned config. Ubuntu + Postfix + Courier IMAP + MySQL + Amavisd-new + SpamAssassin + ClamAV + SASL + TLS + SquirrelMail/Roundcube + Postgrey

Thank you Bud you've been a tremendous help.