Hey guys, more of a web developer here, but I have intermediate-level skills in managing linux, it's been super fun so far!

I just recently got a mail server up and running on my Linux box (CentOX 6.4 x64, mail server is iRedMail) and I've been researching some of the things I need to do to lock it down to avoid spammers taking over my account and getting blacklisted.

My question is, what do you guys consider most important when securing a mail server? If you could link off to an article you love or something, that would be great.

Some steps I've taken:

-Whitelists and Blacklists setup
-SPF setup on the domain's DNS
-Running SSL encryption over the network
-Mail server is not an Open Relay

Ran a test of my server at this address: http://mxtoolbox.com/diagnostic.aspx
and everything passed....

I really think I need to setup a query to SpamHaus or on of the DNSBLs but I'm not entirely sure how to do that.

I have been referencing this article: http://www.vircom.com/security/top-1...-email-server/

But I'm not really sure how to do some of that stuff, a more tutorial-based article would be preferred.

Thanks guys! Any help is appreciated, big or small!

http://wiki.centos.org/HowTos/Amavisd .. this is a pretty common configuration. I use this in conjunction with policyd-weight but there are other policy servers such as postgrey - http://wiki.centos.org/HowTos/postgrey.

Any solutions you know of that don't involve greylisting? In my experience so far, greylisting has queued messages for up to an hour (usually minimum 15-30 minutes) before I actually receive them on my end, and this is just not something I can deal with. I have customers and internal conversations that need to be timely.

Greylisting shouldn't affect many legitimate customers and if it does then they can work around it by relaying all outbound email through their ISP's mail servers. Sending email directly from a SOHO setup in a dynamic range is almost guaranteed to be dropped.