Scott Burton writes:

I have searched around about sendmail tag problems on the list and have found similar answers to my question. However none of them work. ...

I pay close attention to not having any whitespace before the To: and From: headers.

I receive this error from multiple SMTP hosts: 503 must have sender and recipient first Is it possible that you installed ZDebug.

As several people on the list pointed out, ZDebug is incompatible with "sendmail" (at least some ZDebug versions). Dieter PS: I do not like Mime mails in this list, because the stupid mailman installation discards Mime headers in the digest. As a consequence, my mail reader is unable to decode such messages :-(