MS Outlook no longer able to connect to IMAP server

A Windows update can be related, but the documented Outlook-specific causes are narrower than “the update broke IMAP” in general.

For classic Outlook on Windows, the two supported causes/workarounds in this scenario are:

1. App password issue If the IMAP provider uses app passwords, create a new one in the provider’s webmail security settings, then update it in Outlook:
   • In Outlook, go to File.
   • Under Account Information, select the affected IMAP account.
   • Select Account Settings > Server Settings.
   • Paste the new app password into the Password box.
   • Select Next, then Done.
2. TLS 1.3 on Windows 10 Microsoft documented that TLS 1.3 may cause IMAP/POP connection errors on Windows 10, while Windows 11 TLS 1.3 should work fine with Outlook. If the PC is on Windows 10 and the failure started after an update, this is a known workaround:
   • Open Regedit.
   • Go to: Computer\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols
   • If TLS 1.3 exists under Protocols, export the key first so it can be restored if needed.
   • Delete the TLS 1.3 key and its subkeys.
   • Restart Outlook. If sync still does not resume, restart Windows.
   Warning: editing the registry is a high-risk change. Export the key first so the setting can be reverted.

If Outlook is also showing setup-type errors such as Autodiscover failed or Invalid IMAP server info, the next supported step is to get the exact IMAP server name and port from the email provider and sign in again using advanced settings.

If the account is an Exchange Online mailbox being configured in Outlook with IMAP/SMTP, another documented cause is authentication mode: Outlook does not support Modern authentication for POP/IMAP Exchange profiles. In that case, IMAP/SMTP connectivity depends on Basic authentication being enabled for those protocols.

• Outlook IMAP or POP server unexpectedly terminated the connection, and the server was interrupted | Microsoft Support
• Error: IMAP Autodiscover Failed | Microsoft Support
• Error: Invalid IMAP Server Info | Microsoft Support
• Can't connect to Outlook by using POP/IMAP and Modern authentication