Whitelisting mail servers

Hello,

Is there a way to whitelist a mail server so that all mail sent to us by 
that server is accepted, bypassing all other checks, especially Bayes 
filtering?

The problem is with Banks; we are receiving huge amounts of phishing 
mail, so trained Bayes filters tend to become over-reactive, sometimes 
discarding even real mail.

My idea was to whitelist the mail servers of the Banks (if I find out 
how) to ensure that their mail reach us, but if you suggest other ways 
to achieve the desired result, I would appreciate your advice.

Best regards,
Nick