No, you cannot whitelist incoming connections in iptables based on a local user account. You can whitelist based on incoming IP address and to a specific port using the advanced port filtering (see readme.txt).
Thank you for the confirmation.
Very helpful and much appreciated.
I guess that our only alternative is to the move our SMTP mail to another server.
Anybody else have a separate SMTP server for incoming mail (because of strict IP filtering needed for HTTP traffic)?