Hardening postfix for ISPConfig3

This is a set of links with instructions on how to harden a postfix installation used by ISPConfig3.

First the one from HowtoForge:

• Hardening Postfix For ISPConfig 3. Covers Reverse DNS, SPF, Strict rfc, SPF Check, Restrictions, Greylist and DNSBL (DNS Based Blacklist/Blocklist)

And the others from nixCraft:

• Postfix mail server block Malware with blacklist
• Postfix mail server block .bat, .exe .com .vbs mime attachments – common virus spreading files
• Postfix configure anti spam with blacklist