Really hope someone has a solution to this problem.
Email process in plesk (qmail) will be tagged with a number just before the email address in the email header.
Example:
Return-Path: <m.sheabv@stageone.dk>
Delivered-To:
100-email@abc.com.sg
Received: (qmail 18295 invoked by uid 110); 18 May 2004 04:39:24 -0000
Delivered-To:
100-ip@abc.com.sg
Where "email@abc.com.sg" is the catch-all box.
Then a POP3 downloader will collect email from the plesk server to deliver email to the exchange server.
Problems:
1) When someone BCC to a user of abc.com.sg, an error of "NO VALID RECIPIENTS FOR MESSAGE" occur.
2) Same problem when someone send to a mailing list, where a user of abc.com.sg is in the list.
No problem when To: & CC: field has a valid email address of the recipients.
So the tagging of a number before the email address in the email header become an invalid email address when it reach another email server like exchange server, thus resulted in mail delivery error.