Hi everyone again. I receive a email from one user, he tell me that the Emails that he sent are delivered as and attachment, and he tell me that this problem start before the upgrade from Exchange 2003 to Exchange 2010 SP1. I make some test and I found that this only occurs between Exchange Server organization, because if I send the same email to gmail.com account this problem does not occur. I really appreciate your help, I cant fine any possible causes to this.

See what format the message is sent out as? Is the issue between users in the SAME Exch Org or between different Exch Orgs?Sukh