IMAP access to Exchange Online mailbox stopped working
Office 365 (Exchange) Friday, 16 April 2021 by paul

Recently users have been unable to access Exchange Online mailboxes using IMAP protocol and basic authentication.

The reason for this issue is basic authentication is being deprecated and is in the process of being changed from on by default to only being on when a tenant admin allows it.


1. Go to Modern Authentication admin portal: https://admin.microsoft.com/Adminportal/Home?source=applauncher#/Settings/Services/:/Settings/L1/ModernAuthentication

2. Tick the IMAP4 box and save.

Then can authenticate with IMAP within an hour.

This is only a temporary fix as support for basic authentication will be removed from Exchange Online in 2nd half of 2021: https://docs.microsoft.com/en-us/lifecycle/announcements/exchange-online-basic-auth-deprecated

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