AUTHENTICATE failed: AUTHENTICATE failed / LOGIN failed

Microsoft 365 / Outlook.comIMAPPOPSign-in problem

The error usually looks like this:

A1 NO AUTHENTICATE failed.

What it means

Microsoft’s IMAP or POP server rejected your app’s sign-in. Basic authentication (a password) is permanently disabled for IMAP and POP in Microsoft 365, so only OAuth 2.0 sign-ins work.

Common causes

  • The app is signing in with a password (LOGIN, AUTHENTICATE PLAIN or USER/PASS), which Microsoft no longer accepts.
  • The app uses OAuth, but its access token was issued for the wrong resource (such as Microsoft Graph) or is missing the IMAP.AccessAsUser.All or POP.AccessAsUser.All scope.
  • IMAP or POP is disabled for the mailbox.

How to fix it

  1. Decode your access token to check that its audience is https://outlook.office.com and that it has the right scopes.
  2. Check that IMAP or POP is enabled for the mailbox in the Microsoft 365 admin center.
  3. If your app only supports passwords, Auth-Email can sign in with OAuth on its behalf.

Tools to help diagnose it

OAuth token decoder and XOAUTH2 builder

Decode a Microsoft or Google access token, check its scopes, and build or decode XOAUTH2 strings

Email server checker

Check any IMAP, POP or SMTP server’s encryption, certificate and supported sign-in methods

IMAP connection tester

Start a private IMAP test server and watch your email client’s exact connection as it happens

Can’t update your app to use OAuth?

Auth-Email fixes sign-in errors like this one without changing your app, printer, scanner or script. It signs in to Microsoft 365 / Outlook.com with OAuth on your app’s behalf, while your app keeps using a normal username and password over IMAP, POP or SMTP.

Read the docsTry Auth-Email →

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