Mercury/32 ver 4.9

Hi all,
why do I receive the same message inbox more than one, sometimes there can be up to 4 copies in the inbox. This happens when a non-local sender sends a message to more than one email address (to, cc).

Outlook view

Mail folder view

Thanks

How are messages received, through MercuryS or MercuryD? Is it sender dependent or same for all senders?

We use POP3 (MercuryD). This happen for all sender with more than 1 receiver (to ; cc). this does'nt happen when the message is only addressed to one recipient.

With POP3 delivery the original SMTP envelope is lost and the message is presumably duplicated with one copy for each recipient by the intermediate server with only the TO: and CC: headers that are visible in the message itself for Mercury to work with.

Sometimes the host server adds a header for the intended recipient though. This is what Mercury help suggests:

Checking for special headers in messages
By default, MercuryD goes through the standard headers in incoming mail looking for local addresses: the fields it examines are: "To", "Cc", "BCC" and "Received". MercuryD also records the Message-ID of every message it processes and usually will not attempt to deliver the same message twice.
Unfortunately, not all ISPs use POP3 mailbox schemes that will work with this approach: some use a non-standard header to record the address of the person for whom the message was actually intended - for example, "X-Deliver-To" is one that is seen from time to time. If your ISP uses a non-standard header to record the delivery envelope address, you can tell MercuryD about it using the Headers control: type in the name of the header Mercury should examine for local addresses (so, from our example above, you would type in X-Deliver-To). The field is not case-sensitive (so, X-Deliver-To and X-DELIVER-TO are treated as identical) and you can add the colon separator at the end of the name or not as you wish. If your ISP uses more than one special header to identify the local addressee, you can enter multiple header names in this field, separated by semi-colon characters (";" ). You must not type any spaces in this field.
If you check the control labelled Check only in these headers then MercuryD will no longer examine the standard To, Cc, Bcc and Received headers for local addresses and will not discard duplicate messages. Use this control only if you are sure that your ISP always adds the header to your mail.
Your ISP will usually be able to tell you if they use a special header to identify the envelope address in your messages.

I remember this duplicate message problem. IIRC, this is how it was resolved.

Duplicate message suppression (since v4.73):

You can now create an empty file called MSGIDS.MER in any mailbox directory (i.e, a directory where a .CNM file gets created), and this signals to Mercury that it should suppress duplicate messages in that mailbox. Duplicate detection is based on a combination of sender and message-ID, and only the last 200 messages delivered to the mailbox are actually remembered.

Thanks Sir, solved with this guides.