One of our techs ran across this problem and someone posted a fix in Apple’s Support Forums.

Here’s the Support Forum page

In case the link changes/goes down here’s the salient portion of the suggested fix:

Turns out that SL rejects empty subject lines by default. In order to make it play nice I stopped the mail service headed over to:


and turned:

/^subject: *$/ REJECT empty subject header in /etc/


#/^subject: *$/ REJECT empty subject header in /etc/

After restarting mail all worked perfectly.