New outlook isn't syncing IMAP accounts

Question

one of my employe's new outlook for windows 11 stopped syncing suddenly on 21/3/2026, he has been using new outlook for some time with no issues, and 2 of his other accounts still work fine, the problem is with these 2 IMAP accounts, the accounts still sync and deliver messages on the classic and phone versions.

I have tried to repair the accounts and the app to no avail. I updated both windows and outlook.

my problem is that I can't remove and add the accounts again because they contain huge amount of data and it will take several days for them to fully sync if that. I am stumped, I have contacted the admins of the email servers and still no solutions.
I have read through all the Q&As that sounded similar and none worked

has anyone had a similar issue before? can anyone think of Fix without removing/adding the accounts or resting the app?

Answer 1

For IMAP accounts that suddenly stop syncing only in new Outlook while they continue to work in classic Outlook and on mobile, available guidance focuses on connection/IMAP-side issues rather than a client-only repair that avoids any resync. The following steps align with that guidance and minimize disruptive changes as much as possible:

1. Approve any blocked IMAP sign-ins (for Outlook.com–backed mailboxes)

If the affected IMAP accounts are Outlook.com/Hotmail/Live mailboxes (or use Outlook.com as a backend), IMAP connections can be blocked until explicitly confirmed as safe.

1. Sign in to the affected mailbox in a browser.
2. Go to the Recent activity page: account.live.com/activity.
3. Under Recent activity, find the Session Type entry that matches the time the IMAP connection started failing.
4. Expand it and choose This was me to approve the IMAP connection.
5. Return to new Outlook and try syncing again.

This step does not remove or re-add the account and can immediately restore IMAP connectivity if the issue is a security block.

2. Reduce concurrent IMAP connections (if the same mailbox is used in multiple clients)

If the same IMAP mailbox is configured in classic Outlook, new Outlook, and mobile clients, Outlook.com IMAP can hit connection limits and start returning errors.

• After approving the session as above, temporarily close or sign out of one or more other IMAP clients (for example, exit classic Outlook or disable the account on the phone) and then test sync in new Outlook.

3. Confirm correct account type and IMAP configuration in classic Outlook

Because the same accounts still work in classic Outlook, use that working configuration as a reference:

• In classic Outlook, open Account Settings for the affected addresses and verify:
  • The account type is correct (for example, Outlook.com addresses should be configured as Outlook.com, not Exchange or Microsoft 365).
  • For IMAP accounts such as Gmail/Yahoo/ISP mail, ensure Require logon using Secure Password Authentication (SPA) is unchecked on the IMAP details page.

If SPA is incorrectly enabled or the account type is wrong, it can cause inconsistent behavior across clients. After confirming the configuration in classic Outlook, restart new Outlook so it can refresh credentials and connection parameters. This does not require deleting the account in new Outlook.

4. If the IMAP server is Outlook.com and uses a non-Microsoft domain

If the mailbox is accessed through Outlook.com but uses a domain other than @live.com, @hotmail.com, or @outlook.com, IMAP sync issues are a known limitation.

• The documented workaround is to remove the connected IMAP account in Outlook.com and reconfigure it as POP instead. This change is server-side and will require a new download of mail, so it does not meet the requirement to avoid resync, but it is the supported resolution when the root cause is Outlook.com IMAP limitations.

Given the available documentation, any fix that completely avoids re-adding/re-syncing the IMAP accounts is limited to:

• Approving blocked IMAP activity via the Recent activity page.
• Ensuring correct account type and IMAP settings (especially SPA) based on the working classic Outlook configuration.
• Reducing concurrent IMAP connections from multiple clients.

If these steps do not restore sync in new Outlook and the provider is Outlook.com with a non-Microsoft domain, switching the account to POP or re-adding it remains the documented path to resolution, even though it involves a full resync.

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References:

• POP, IMAP, and SMTP settings for Outlook.com
• Troubleshoot Outlook email setup
• I can't send or receive messages in Outlook