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One of our clients has been having problems where whenever an external email has multiple recipients on their domain, each recipients receives it a matching number of times (see below). This only occurs for emails originating from outside the company.

  • To: 1 user; 1 email received
  • To: 3 users; 3 emails received per user.
  • To: 1 user (+1 gmail address); 1 email received per user.
  • To: 2 users (+1 gmail address); 2 emails per user (1 email to gmail)
  • To: 1 user, CC: 1 user; 2 emails per user

This is an up-to-date Exchange 2003 Server (SP2) on an SBS2003 Server. The Exchange server connects to the MTA via POP. The Exchange databases are not near their capacity. All email scanning is disabled in McAfee.

We have checked with the MTA and only one email is being sent to the Exchange server per user.

I have set up 3 test accounts to eliminate any chance of it being related to rules that have been set up specific to users in either Exchange or Outlook.

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How are your POP3 accounts configured? Is there one mailbox per user or a catchall mailbox? By the way, BCc has problems when used with the POP3 connector for Exchange, where a catchall mailbox is involved. –  Chris McKeown Oct 3 '12 at 11:42
    
It's a chatchall mailbox. BCCs haven't been mentioned as causing any issues, and I didn't use any in my testing –  Miles Hayler Oct 3 '12 at 11:57
    
BCC basically won't work with a catchall mailbox and the POP3 connector due to the way POP3 works - information here. The problems you're facing are possibly a result of using a catchall mailbox too. Can you not switch to using per-user mailboxes, or better yet, host your own MX? –  Chris McKeown Oct 3 '12 at 12:00
    
Cheers for the info, although BCC is outside the scope of the current problem. This is a client we took over from another company. I will investigate moving them to per-user mailboxes. In the meantime, can you think of anything else that could be causing this? –  Miles Hayler Oct 3 '12 at 12:07
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1 Answer

up vote 2 down vote accepted

I would bet that the issues you're experiencing are related to the way that the POP3 connector for Exchange works, and the fact that you're using a catchall mailbox.

You mention that you're using a catchall POP3 mailbox - can you look at this remotely before you pull the mail down? You might find there are three copies of the same email copied to three different people. Since there are no individual mailboxes for those recipients, they all get dumped into the same mailbox.

As as aside, I would avoid using the POP3 connector because BCC recipients don't work with it when a catchall mailbox is involved.

Can you switch to one mailbox per user, or maybe host your own MX?

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I think you could be right. Further research both on the internet, and on the email message headers leads me to believe that the message originator creates (for example) 3 emails for 3 users and sends those. The header from field contains the intended recipient of the specific message and the header to field contains all 3 recipients. These 3 messages end up in the catchall mailbox and are pulled into Exchange which looks at the to field which contains all 3 email addresses and sends it to all three. It repeats this for the other 2 emails. –  Miles Hayler Oct 3 '12 at 12:55
    
X-Barracuda-Envelope-From: m.hayler=milestest2=recipientdomain.net=igpjopef@originatordomain.co.uk ----------------------------------------- To: "Miles Test1" <MilesTest1@recipientdomain.net>, <milestest2@recipientdomain.net>, <milestest3@recipientdomain.net> –  Miles Hayler Oct 3 '12 at 12:57
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