SBS 2003 Share Fax issue

I have a share fax that is recently acting up. When a user is sending fax using a distribution list in Outlook 2003. Outlook adds a prefix with the company name followed by the @ sign and the fax number. Then fax would NOT send. And in some other contacts that only the fax number is being used with the right prefix. The fax will send no problem.

How can I fix this issue?