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
    2023-01-02T18:49:37+00:00

    It works for me, thanks great

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  2. Anonymous
    2023-01-02T16:51:21+00:00

    Regarding theories: there is some non-determinism at work. This morning, everything was working normally, as it had been for months. Then I suddenly ran into this error message. After trying a few times, I was able to connect once. However, all subsequent attempts kept failing.

    To me this suggests that it is related to rate limiting code. At https://stackoverflow.com/a/55190289, the first likely reason for receiving this message: “It is a Microsoft's mechanism to shut down chatty clients. The solution would be to login to this account less frequently.”. With IPv6, determining if two connections belong to one person or network cannot be done with the same strategy as with IPv4. Most individuals/networks have a large range of IPv6 addresses available to them whereas with IPv4 the individual or network would only have on IP address. So attempts to rate-limit IPv6 addresses often work in large ranges of addresses which might represent just one individual/network or a large number of distinct users who should not be placed together in the same rate-limiting bucket. For example, Microsoft might be using the first 32 bits of the address as a rate-limiting bucket key. If someone owns an IPv6 /120 subnet, they could test if only having one IMAP client in that subnet connecting to office365 works for them because they could guarantee that client’s most significant 32 bits are globally unique.

    If anyone who is able to open tickets does get a proper explanation back from Microsoft when they resolve this, that’d be intriguing to hear!

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  3. Anonymous
    2023-01-02T16:49:48+00:00

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