[Mimedefang] Small syntax question

[NFN Smith]

I'm updating my MD configs to exempt submissions by trusted users from 
SpamAssassin scanning.  By "trusted", I mean users that authenticated 
themselves with SMTP AUTH, and have submitted via the MSA daemon on 
ports other than 25.

I'm still novice enough at perl code that I don't quite have this working.

What I've done is to add code to sub filter_end, following the default 
exit, if the message has been rejected:

sub filter_end ($) {
     my($entity) = @_;

     # No sense doing any extra work
     return if message_rejected();

     # If the message has been submitted via the MSA daemon (that is,
     # an authenticated user, on ports 465 or 587), exempt
     # from SpamAssassin scanning.  If the message is submitted with
     # the MTA daemon on port 25, then scan.

md_graphdefang_log('=== macro check', $SendmailMacros{daemon_name});

     return if ($SendmailMacros{daemon_name}) = "MSA";


My log entries are showing that it's correctly telling which service has 
been used to submit the message, but my "return if" syntax isn't 
correct, and the result is that whether the daemon_name is "MTA" or 
"MSA", the return is being executed.  In short, this is completely 
disabling all calls to SA.

What's the correct syntax to do what I'm doing?

TIA

Smith