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Outlook not syncing: getting email, calendar, and contacts back in step

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When Outlook does not sync, offline mode is usually on, the saved password is no longer valid, or the account is set up wrongly, for example as POP3 instead of IMAP. In classic Outlook with Microsoft 365 or Exchange, rebuilding the local cache often helps. A plain IMAP account never syncs calendar and contacts.

1. Check the connection, offline mode, and webmail

Does the status bar at the bottom show “Working Offline” or “Disconnected”? In classic Outlook, turn offline mode off again under Send / Receive > Work Offline. Also sign in to your provider’s webmail: if the new emails are there, the problem is Outlook. If they are missing there too, the mailbox is often full or the fault lies with the provider.

2. Enter the password again

After a password change or switching on two-factor sign-in, the server rejects the saved password. Outlook then keeps asking for the password or simply stops syncing. Enter the current password. Many providers require a separate app password for Outlook when two-factor sign-in is on. With some providers, such as GMX and WEB.DE, IMAP access must also be allowed in the mailbox settings.

3. Use IMAP instead of POP3

With POP3, Outlook downloads emails to the computer and, depending on the setting, deletes them on the server. They are then missing on the phone. IMAP keeps all devices in step. If an account is set up as POP3, add it again as IMAP after backing up the existing emails.

4. New or classic Outlook

The new Outlook for Windows syncs accounts from other providers through the Microsoft cloud. If syncing gets stuck there, removing the account and adding it again often helps. In classic Outlook, you find the account under File > Account Settings > Account Settings, where many account types also offer “Repair”.

5. Classic Outlook with Microsoft 365 or Exchange: rebuild the cache

  1. 1Under File > Account Settings > Account Settings > Data Files, check where the account’s .ost file is, usually in %localappdata%\Microsoft\Outlook.
  2. 2Close Outlook completely.
  3. 3Rename the .ost file, for example to “old.ost”.
  4. 4Start Outlook. It downloads the mailbox from the server again, which takes a while for large mailboxes.
  5. 5Once everything works, you can delete the renamed file.

6. Calendar and contacts

A plain IMAP account only syncs email. Calendar and contacts stay in step between PC and phone when the account supports it, such as Microsoft 365 or Exchange. With other providers it depends on the provider and the Outlook version: the new Outlook, for example, also syncs calendar and contacts for Gmail. Outlook for Windows does not support CalDAV and CardDAV out of the box.

Frequently asked questions

Why are no new emails arriving in Outlook?

Often offline mode is on, the saved password is invalid, or the provider requires an app password. A look at Outlook’s status bar and at the provider’s webmail usually shows the cause.

Why are emails missing on the phone that are on the PC?

Usually the account on the PC is set up as POP3 and takes the emails off the server. With IMAP, all devices stay in step.

Do I lose emails when rebuilding the cache?

As a rule, not with Microsoft 365 and Exchange, because the emails are on the server and are downloaded again. Local archives in .pst files are separate. Just check beforehand whether emails are still waiting in the Outbox.