I can't answer your question directly, as I have not had that probelm. But a great resource site is www.securitysage.com.
They offer free advice and configure files for Postscript.
Just remember to only change one setting at a time. Also, are you confusing PostFix with IMAP? With netscape, if it fails when trying to 'read' mail, then it is IMAP, but if it fails when sending mail, then it is PostFix.