messages on hold

[Simon Jones]

Hiya, I'm getting a lot of entries in the maillog with messages on hold.
Anyone know why this could be happening?  Or where to start looking to
see if I do actually have a problem, thanks!

Here's an example;

Aug 14 09:33:45 gate1 postfix/cleanup[3509]: CD5A26DB42A: hold: header
Received: from [81.26.189.95] (unknown [81.26.189.95])??by
gate.domain.co.uk (Postfix) with ESMTP id CD5A26DB42A??for
<recipient at domain.co.uk>; Tue, 14 Aug 2007 09:33:45 +0100 (BST) from
unknown[81.26.189.95]; from=<sender at domain.com> to=<
recipient at domain.co.uk > proto=ESMTP helo=<[81.26.189.95]

SMJ