Qmail - Block mail hosts by wildcard, name or IP?

Here is what I have to work with.
Redhat,Qmail,Clam,SpamAssassin on a VPS with Plesk 7 and multiple domains.
Question - Can I somehow block all mail server in the world but let through only the ones I want. I need to do this at the domain level. For example maybe domain A needs to do this but domain B should still accept all connections from any mail server. If this cannot be done with any of the above software is there a firewall or other software that do this. Remember the setup will be different for each domain and the all use the same Qmail.

I do not know much about Linux but if I can do this somehow I will move my domains to a Linux VPS. Also someone said that Plesk will not allow mail users to change their own password. Is this true?

Thanks in advance,
Possible Windows convert

 

 

 

 

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