Removing duplicate messages

How to find and delete duplicate messages in a mailbox.

Duplicates usually turn up after folders have been merged, or after a mail program has downloaded the same messages more than once. Zimbra has no tool of its own for clearing them, so the practical route is a Thunderbird extension working against your mailbox over IMAP.

What you need

Install Thunderbird, then add the Remove Duplicate Messages extension. Connect Thunderbird to the mailbox over IMAP rather than POP, so it acts on the copy held on the server.

Clearing the duplicates

1. Open each folder once. Thunderbird needs the message headers before it can compare anything, and it only fetches them when a folder is opened.
2. Right-click the account name at the top of the folder list, above the Inbox.
3. Choose Remove Duplicate Messages.

You can set what counts as a duplicate, using the sender, subject and message identifier, and optionally the message body for copies whose headers differ. The extension works through the folder you picked and everything beneath it.

Before you confirm

Thunderbird is connected over IMAP, so anything it deletes is deleted on the server. The change reaches every device you read your mail on, and there is no separate local copy to fall back on.

Read the list it offers before accepting it, and start with a single folder rather than the whole mailbox until you are satisfied it is matching what you expect.