What is the exact error message?

I have submitted the full error message but no response to date. Any ideas?

Where did you post the error message? It's not in this thread.

Sorry, my fault - I sent it as a reply to your email which, of course went into your null box instead of the thread.

The error message is: The following message to <cecarle@live.ca> was undeliverable. The reason for the problem: 5.1.0 - Unknown address error 550-'Requested action not taken: mailbox unavailable'

Reporting-MTA: dns; idcmail-mo1so.shaw.ca

Final-Recipient: rfc822;cecarle@live.ca Action: failed Status: 5.0.0 (permanent failure) Remote-MTA: dns; [65.55.92.168] Diagnostic-Code: smtp; 5.1.0 - Unknown address error 550-'Requested action not taken: mailbox unavailable' (delivery attempts: 0)

Note that the correct address is in the list of recipients to whom the messages are sent but, without fail, always returns this error message.

I'm a bit at a loss with this. Are you saying the recipient with the @shaw.ca email address is getting your message, and you get the error message for the @live.ca email address upon sending a message to the list address?

Can you double-check your mailing list? Look for potential spelling mistakes.

Do you have an entry with 'cecarle' as an email address in your mailing list?

If you are at a bit of a loss imagine how I feel! :-) The intended recipient has an @shaw.ca address and I have triple checked the mailing list. Despite the mailing list being correct and otherwise containing NO @live.ca addresses I routinely receive the error message when I send a message to the list. And yes, the intended recipient is cecarle@shaw.ca. That is the address in the list. I will check with the intended recipient to see if they do actually receive a copy. I have not done that yet.

I am pretty confident I have now resolved this issue. It would appear that although the recipient uses an @shaw.ca address mail to that address is also being forwarded to an (old) @live.ca address. They have deleted their @live.ca address but must have left the auto-forwarding enabled at shaw.ca so that a copy of any email was being forwarded to an address which no longer exists. Thanks for your help. I trust we are no longer at a loss but have learned a lesson in how auto-forwarding can fool us.

Please note that Shaw.ca and live.ca use the same servers. I have at times been prompted about the shaw.ca SSL certificate offered to me by hotmail. Interestingly enough I live in Australia, so I really find the live/hotmail/shaw thing messed up.

You may have found the answer in your case, but Microsoft and Shaw appear to be the same physical hardware