Find the duplicates in your mailbox

How it works

1. Enter your mailbox credentials — address, password (or app password) and IMAP server settings.
2. MailSync scans read-only — the connection is opened without write access, and only the technical headers of your messages are read: unique identifier, sender, recipient, subject, date and size. Never the contents.
3. You get a detailed report — number of duplicates, space you'd recover, breakdown per folder, a preview of the largest groups, and the list of folders left out of the scan with the reason for each.
4. You confirm, or you don't — a single click moves the extra copies into a dated folder in your mailbox. Without that click, nothing moves.

Nothing is deleted, ever

This is how the tool works, not an option you tick. Extra copies are moved into a folder in your mailbox named MailSync/Doublons followed by today's date. They stay readable, browsable and recoverable from any mail client.

In practice that means two things. First, undoing is in your hands: just move the messages back where they were, or move the folder elsewhere. Second, space isn't freed immediately: it will be freed when you empty that folder, once you've checked that nothing important is in it. That's a deliberate trade-off — better to wait a few days to reclaim space than to lose an email for good.

How a duplicate is recognised

Every email carries a Message-ID in its headers, a unique identifier assigned when it was created. Two copies of the same message share it; two different messages never do. That's the primary criterion, and it's what makes detection reliable rather than approximate.

Some messages don't have one: those imported from an mbox archive, certain drafts, exports from older software. For those, MailSync computes a fingerprint from the sender, recipient, subject, date received and exact size in bytes. Those are precisely the messages where duplicates get created — an import run twice, a migration replayed — so ignoring them would have stripped the tool of its purpose.

Which copy is kept

The copy that's kept is the one sitting where you'd go looking for it. The order of preference is: inbox, then your own folders, then Archive, then Sent. When two copies tie, the oldest survives: that's the original, the one your already-sent replies link back to.

Folders left out of the scan

Four categories of folder are never scanned, and that's what protects your organisation:

• Virtual folders — in Gmail, "All Mail" contains a copy of every message in the mailbox. A message labelled "Work" appears at the same time in the inbox, in the Work label and in All Mail: those are three views of one message, not three copies. Scanning it would mean seeing a duplicate for absolutely everything.
• Trash — whatever you put there, you've already sorted.
• Spam — junk mail contains near-identical messages by nature, and there's nothing to gain there.
• Drafts — two similar drafts are working versions, not duplicates.

The report always shows the list of folders that were scanned and the list of those left out, with the reason for each exclusion. You check the scope before you confirm, not after.

Typical uses

• An import run twice — the most common case: a Google Takeout archive imported once, then imported again because you weren't sure it had worked.
• A migration replayed — a transfer that was interrupted and restarted from scratch leaves two copies of the part already moved.
• A misconfigured POP account — several devices polling the same mailbox without marking messages as read end up accumulating copies.
• A merge of two mailboxes — after combining an old address with a new one, the overlapping period exists twice.
• A mailbox that's full for no visible reason — when the quota is hit while the message count looks reasonable, duplicates are often the cause.

What the tool doesn't do / limits

• It deletes nothing — and therefore has no way to free space on its own. The set-aside folder is yours to empty.
• It doesn't compare message contents — two emails with identical content but rewritten by a server (new Message-ID, different size) won't be seen as duplicates. That's a choice: comparing contents would mean downloading every message and would produce false positives on automated notifications.
• It doesn't deduplicate across two different mailboxes — the tool works inside a single mailbox.
• It can't be scheduled — every pass is triggered by you, with a report to approve.
• It doesn't touch the excluded folders — trash, spam, drafts and virtual folders are left exactly as they are, even if they contain duplicates.

Pricing

The scan and the report are free, with no account and no size limit: you know what you have before committing to anything. Setting duplicates aside is free up to 5 GB of duplicates found. Beyond that it costs €5.99 for this operation, or it's included with no limit in the Premium subscription. The threshold is about the volume processed: it's the same for everyone.