I have an exchange 2007 installed with content filter activated and also the antispam feature, and sometimes i have user saying that there are complains from people that are trying to send email to them that they get the following message:
Reason: SMTP transmission failure has occurred
Diagnostic code: smtp;554 5.6.0 Invalid content
Remote system.........Microsoft ESMTP MAIL Service ready at Wed, 16 Jan 2013 15:39:26 +0100)
Any ideas on how to solve this issue?