I had an external non-user contact me regarding an error message she received trying to send information to a recipient within our domain. We do have Reverse DNS, and proper MX record checks set up however she had no problem sending it to other people (myself) within our domain. Unfortunately I have limited information on this users setup but she did forward me the error message she received.
I realize that this question has been asked in the past however it may need a new light shined on it. Possible explanation from another thread.
"Re: Pop-before-SMTP #4 Jul 19th, 2004 | Add to DMR's Reputation | Flag Bad Post
The POP-before-SMTP authentication scheme usually has a time limit associated with it. If you haven't authenticated to the POP server (by checking your mail) within the specified timeout window, you may get the 550 error. The next time it happens, try checking your mail first and then resend the message. "
Here is the error she receives while sending information sometimes:
You do not have permission to send to this recipient. For assistance, contact your system administrator.
<sub.domain.com #5.7.1 smtp;550 5.7.1 <xxx@domain.com>... Relaying denied. Proper authentication required.>
I have put in generic names for privacy concerns. I realize the issue is most likely the external users issue however I'm doing this as a favor to her. If anyone has any suggestions I would be much appreciative.
Thank you,
Brian