We are running Exchange Server 2003 SP2 and using Outlook 2002 as the client. I have a user who cannot receive email from a particular sender, but only if she is one of several recipients of the same email. In other words, if she is the only recipient she gets the email, but if she's part of a group of several recipients, the sender gets an error message that the email can't reach my user.
The error message that the sender gets is as follows:
There was an SMTP communication problem with the recipient's email server. Please contact your system administrator.
<xxxx.org #5.5.0 smtp;550-mail.xxxx.org (xxxx.org) [IP address]: is currently not permitted>
I have many users who receive emails when they are part of a multiple recipient message with no problems, so I tend to think the problem lies with the sender's server. Any suggestions as to what I can tell the sender to check for, if it is indeed their problem?