I became recently surprised when I tried to send mass email from my phpBB2 forum. I got the following error message:

General error Ran into problems sending Mail. Response: 550 5.1.2 : Recipient
address rejected: Domain not found

DEBUG MODE

Line : 142
File : smtp.php

==========

Opening this file I found the line 142 code as below:

\tab\tab\tab fputs($socket, "RCPT TO: <$bcc_address>\\r\\n");\par

How could I solve this problem?
Thanks a lot.