Email format problem

I was wondering if anyone knew the answer to this problem I am having when we receive conformation emails from Fed Ex. I get the following message to the administrator mailbox.
The following recipient(s) could not be reached:
joesmoe@domain.com charset=”us-ascii”
The format of the e-mail address is incorrect. Check the address, look up the recipient in the Address Book, or contact the recipient directly to find out the correct address.

if someone knows, please let me know.Can’t find much about this problem anywhere as if I am the only one experiencing it.

Thanks