I suggest using Postfix. I use it and have had no problems that weren't user error. Granted you will have to relearn a lot of stuff, but I think it'll be worthit. To get you started on a security configuration, I'll post my config. My security configuration blocks about 90% of spam, so almost nothing gets through. You might want to install and configure spamassassin as well for spam that does get through. As a small tidbit, in case you don't know anything about Postfix yet, you want to configure your domains to use virtual domains.
At the end, the clamsmtp thing you see is email virus scanning by ClamAV. You can see how to set it up here. I'd recommend more tutorial and documentation sources for you, however you found the jackpot, and all you'll ever need. Good luck!
# Security related config
smtpd_helo_required = yes
disable_vrfy_command = yes
# clamsmtp email virus scanning
content_filter = scan:127.0.0.1:10026
receive_override_options = no_address_mappings