Why does Outlook receive a Content Unacceptable error on send?

Question

A user is using Windows 7 with Outlook 2010 SP2 and emails going through a Jerseymail POP3 setup.

He is receiving a bounce back as soon as he clicks send.

The following recipient(s) cannot be reached: 550 5.6.0 Content unacceptable.

This started a couple of days ago and not to all people he emails out to. Checking the content, there is nothing untoward.

I have had one occasion when I deleted the subject and typed it back in and the email sent, but I have not had this luck with others.

I seems like it is an Outlook issue as the Bounce backs are received very quickly. How could I solve this problem?

Answer 1

550 5.6.0 Content unacceptable. more sounds like an error message from your SMTP server, suggesting it follows some kind of policy of not accepting messages following assigned criteria.

Common criteria might include types of attachments (e.g. not accepting *.doc-files for malware control), used phrases commonly used for spam or fishing mails, etc.

If there's no way contacting the operator of your SMTP server for clearance, try stripping the message down and filling it back up to your failing mail (i.e. try sending a plain message without attachments, then try it with the whole text, if this fails try it with a minimum text and attachments [if it works you should try with variations of the text], if not, try with attachments added [if this fails, it might be caused by the attachments], etc.).