Move your contacts and calendars to another account

How it works

1. Enter your two accounts — the https address of the server, the username and the password on each side. With most providers you need an app password, not your everyday password.
2. MailSync finds the service on its own — first at the address you gave, then at the standard location /.well-known/carddav (or /.well-known/caldav), and finally by walking up to the list of your address books and calendars.
3. The inventory happens before a single write — we list what exists at the source, and above all the unique identifiers (UIDs) already present at the destination.
4. Only what is missing gets copied — a contact or an event whose UID is already there is skipped, never replaced.
5. You get a report with real numbers — copied, duplicates skipped, items without an identifier, failures. Nothing vague.

Two locks against overwriting, not one. The first is the inventory of destination UIDs. The second is technical: every write carries an If-None-Match: * header, which asks the server to refuse if the resource already exists. Even if the inventory had missed something — an address book edited during the operation, say — the server itself will replace nothing.

The content is not touched up. Every vCard and every event is passed on exactly as it was received. We read one single line in it, the UID. A contact photo, a custom field, an exotic recurrence rule, an event attachment: everything goes through intact, because nothing is rewritten.

Use cases

• Leaving one provider for another — your emails follow with the mailbox transfer, your contacts and calendars follow with this one.
• Bringing iCloud home to a Nextcloud — or the other way round: both speak CardDAV and CalDAV, and an app-specific password is enough on the iCloud side.
• Merging two accounts into one — after an address change, gathering into a single address book what used to live in two, without creating duplicates.
• Keeping a copy on a second server — re-runnable as often as you like: what is already there is never copied again.
• Checking a migration done elsewhere — running the transfer afterwards copies only what was genuinely missing, and the report puts a number on it.

What the tool does not do / limits

• Google is not supported. Its CardDAV/CalDAV access requires OAuth; Google app passwords only cover IMAP and SMTP. For now, the manual export/import through Google Contacts and Google Calendar remains the way to go.
• Microsoft 365 and Outlook.com are not either. They expose no CardDAV or CalDAV service at all: it is not an authentication problem, the protocol simply does not exist on their side.
• One destination collection per type. All contacts land in the first address book of the destination account, all events in its first calendar. To target another one, paste its exact address in the collapsible block of the form. We prefer that predictable behaviour to an automatic matching between address books, which would be guesswork.
• The copy goes one way. Nothing is sent back to the source, nothing there is modified or deleted: it is read, and that is all.
• Items without a UID are left aside and counted separately. Without an identifier, every re-run would add another copy.
• Only https is accepted, and the address must be that of a server reachable from the public Internet: a local network address is refused, as is an address containing credentials.
• Free up to 200 items written, contacts and events combined — the same threshold for everyone. Beyond that the transfer stops and tells you so; just run it again, or lift the cap with a subscription.