Emails to multiple recipients get delivered multiple times per user

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.

Solution 1:

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?