Thunderbird IMAP responded: User is authenticated but not connected

Anonymous
2022-12-27T12:29:12+00:00

Since yesterday, my Thunderbird client cannot connect to the outlook.office365.com IMAP server and other users at my university are also having this problem. I have deleted the stored token and redone the connection procedure but it does not work. I get two error messages:

The current operation on 'inbox' did not succeed. The mail server for account ... (IMAP) responded: User is authenticated but not connected.

Server outlook.office365.com has disconnected. The server may have gone down or there may be a network problem.

This does not work on any platform: Windows, Linux or Macos. Via the browser, we can access the emails but it is a workaround because it does not support openPGP. We need Thunderbird

Outlook | Web | Outlook.com | Account management, security, and privacy

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Anonymous
2022-12-28T22:03:29+00:00

Hi Glenn,

Which version of Thunderbird are you using.

I have 102.6.1 which is the latest one. Can you try updating it if its not and then check.

Also under Thunderbird --> Click on the gear icon on the bottom left bar --> General --> Config Editor --> Show All

Type network.dns.dis in the search field

Select the very first option and click on the toggle arrow on the right, make it true

Close and reopen Thunderbird.. See if this helps

Let me know how it goes

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Anonymous
2022-12-28T21:34:14+00:00

Yes, it is worked for me too!

I just disabled ipv6 netwotking in thunderbird advanced configuration editor (network.dns.disableIPv6 = true)

and it is works again like a charm!

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  1. Anonymous
    2023-01-03T04:55:25+00:00

    Yes, since Christmas, it seems that a range of clients can't receive MS Outlook mail via IPv6. It's not just Thunderbird. Regarding the workaround posted here, you really don't need to globally disable IPv6 in your Thunderbird config. Just add office365.com to network.dns.ipv4OnlyDomains.

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  2. Anonymous
    2023-01-05T04:53:31+00:00

    It looks like Microsoft just fixed it in the last few hours! Yay!

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  3. Anonymous
    2022-12-29T18:05:42+00:00

    The fact that the IPv6 handler on Microsoft’s side is behaving differently than the IPv4 one pretty clearly indicates that this is an issue on Microsoft’s side. It is not Thunderbird that is affected, but all IMAP clients which are doing the right thing and following Microsoft’s DNS records which say how to access the IPv6 endpoint for the service.

    What is more likely is that Microsoft broke some IPv6-specific code such as CIDR validation or IP address range handling (such as ratelimiting and throttling controls which are much harder to implement correctly for IPv6 endpoints than IPv4 ones).

    Anyway, if the issue is that IPv6 IMAP access is broken, Microsoft should be the one implementing the workaround by removing the IPv6 addresses from the record for outlook.office365.com. But that will break it for anyone without an IPv4 address who is using a protocol different from IMAP to access the service. So, really, Microsoft just needs to fix their IPv6 endpoint.

    Please give us some official response, Microsoft!

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