Here is what I need.  I need the ability limit the IPs allowed for authentication on POP, IMAP and SMTP on a user by user basis.  Example Lets say I have the email dave@davesdomain.com  I should be able to limit only the IPs 98.0.0.0/16 and maybe 72.0.0.0/16 to be able to authenticate under his account. Or even set limits for the whole domain.  I need to be able to specify exact IPs, or even blocks or ranges.  ( similar to firewall settings ).  I know this is not a perfect solution to security, but limiting the IPs to connect to a given account greatly reduces the exposure to dictionary attacks.  Also some security settings that would automatically add IPs to the global block list when they attempt to authenticate as a user who should not be connecting from that IP.  I don't want to hear the whole force more complex passwords answer either.  Been there,  It doesn't matter when users tend to use the same complex passwords accross multiple sites.