> However, the mailtpl item just after the
> filter was missing its seperator sign (the ">>>") and the INFO message
> thus became part of the content filter (and I am surprised that it
> didn't create an error).

That's it then. Because of the typo, your content filter was set to reject any message containing:

> Sincerely,

And this also appeared in the rejected message. QED.

  Eric