Eran,

This behavior is by design. SpamFilter will never accept emails unless the recipient domain is in your local domains folder.

There are two exceptions to this, so that SpamFilter can be used as an "outgoing smtp server". The first is to specify the IPs allowed to relay in the IP whitelist you found. The second is to use SMTP Authentication. If a user authenticates correctly, they will be whitelisted and can use SpamFilter to relay.

IMAP is a different protocol that does not get processed by SpamFilter. I'm not sure I understand that problem, as your users are accessing IMAP on different server (or different IPs/ports than SpamFilter). It is the IMAP server that then delivers the emails, not SpamFilter. And if by any chance the IMAP server then needs to use SpamFilter to send emails, all you need to do it to add the IMAP's server IP to the IP whitelist so it can relay.