I see in the smtp-logfile that Firemail sends two sets of RCPT TO-commands.
2011-10-17 19:55:40 127.0.0.1 localhost SMTPSVC1 WIN-EU8SJJT0VPK 127.0.0.1 0 RCPT - +to:+<validmail@domainname> 250 0 31 29 0 SMTP - - - -
2011-10-17 19:55:40 127.0.0.1 localhost SMTPSVC1 WIN-EU8SJJT0VPK 127.0.0.1 0 RCPT - +to:+<> 501 0 27 11 0 SMTP - - - -
I've also tried clearing the TO-recipients:
myFiremail.To.Clear()
And the TO-recipient is only added ONCE in code:
myFiremail.To.Add("validmail@domainname")