[German]At the turn of the year 2022/2023, Microsoft has deactivated Basic Authentication for Exchange Online. This forced Thunderbird users into connection issues with mail servers via IMAP. Thunderbird reports that the user is authenticated (via oAuth2) but is not connected. But there is a workaround for Thunderbird. Addendum: It seems that Microsoft has fixed the issue.
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Basic Authentification abgeschaltet
In the article Reminder: Basic Authentication in Exchange Online will be switches off in 2023, I pointed out that Microsoft will finally switch off Basic Authentication in Exchange Online at the turn of the year 2022/2023. This means that all clients that want to access Exchange Online mailboxes via IMAP will have to switch to oAuth2 (Modern Authentication).
IMAP connection goes on strike in Thunderbird
However, there is the problem that the IMAP connection to Exchange Online via oAuth2 in Thunderbird is on strike. The issue was brought to my attention by two readers.
Reader report #1: Thunderbird fails with oAuth2
Within my German blog reader Klaus left the following comment, reporting issues with Thunderbird IMAP connection since the end of 2022 (I've translated the comment).
Since the day before yesterday the IMAP access with Thunderbird to a MS365 account is not working.
Error message: User is authenticated but not connected.
The tenant admin says the license is active and IMAP is allowed.
Blog reader Theo gave the advice to switch to oAuth2 after all and if there were problems, try the flag:
network.dns.disableIPv6 = true
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on a trial basis. This advice to disable IPv6 brought success. Theo referred to the Microsoft Answers forum post Thunderbird IMAP responded: User is authenticated but not connected, where the topic is discussed.
Reader report #2: Thunderbird
fails with oAuth2
Yesterday, German blog reader Volko N. emailed me and also addressed the Thunderbird Exchange Online login issue. Volko wrote (I've translated the comment):
Problems accessing office365 email servers via IPv6 + workaround.
In case you haven't heard it elsewhere, here's a short info about a "capital buck" Microsoft shot regarding Outlook between the years:
After the announced deactivation of Basic Authentication, suddenly, despite using "OAuth2" as authentication method, the access with Thunderbird via IMAP to my business (Office365) email address was no longer possible, I went troubleshooting […].
As it looks, the error only occurs when accessing the office365 email servers via IPv6, so it does not occur with a pure IPv4 internet connection.
Volko also referred to the Microsoft Answers forum post Thunderbird IMAP responded: User is authenticated but not connected, where , where the solution can be found. Volko writes:
I can confirm that the workaround described there for Thunderbird works for me, namely in Thunderbird via.
Settings -> General -> Edit configuration
under "network.dns.ipv4OnlyDomains" the domain "office365.com".
Maybe it will help one or the other person concerned. Thanks to Theo and Volko for the hints.
Issues fixed by Microsoft
Addendum: Blog reader Volko informed me on 6 Jan 2023 that Microsoft had fixed the problem in the meantime. On January 5, 2022, there was the following entry from Seye_Kuti in this Microsoft Answers forum thread:
This started working for us with IPv6 this morning. Not sure what Microsoft did to fix it.
Das wurde durch weitere Nutzer und Blog-Leser Volko bestätigt. This was confirmed by other users and blog reader Volko.
Similar articlesl:
Thunderbird 102: IMAP-Problem bei Microsoft Exchange/MS365 (oAuth2)
Thunderbird 102.2.0 released – many bugfixes but issues
Reminder: Basic Authentication in Exchange Online will be switches off in 2023
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Hi Günter and thank you for the fix, it works! I have been looking for a solution for several weeks without success.