Recently we discovered that a single customer was unable to send emails to anyone in our domain. However, she was able to successfully receive mails from all users in our domain Also, all other users in her domain did not have a problem sending mails to our domain, it was just this single account.
The error message she received back was: #5.0.0 SMTP; 550 Requested action not taken: mailbox unavailable> #SMTP#.
As mentioned, she receives this error when sending mails to any user in our domain.
We are currently running MS Exchange 2003 on a Windows 2003 domain.
Does anyone have any idea why only a single user would be unable to send mails to our domain? Her individual user account is not blocked on our Exchange server or by the firewall.
I am not fully proficient on the server side, being desktop support, but have been asked to look into the matter by my manager. I do though have access to the servers to check solutions.
Any help would be greatly appreciated.