Outlook.jp IMAP connection fails in Thunderbird and FairEmail

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Outlook.jp IMAP connection fails in Thunderbird and FairEmail

human wild 0

My Outlook.jp account works normally in Outlook Web, including sending and receiving emails. However, all third-party email clients, including Thunderbird and FairEmail, fail to establish an IMAP connection.

OAuth2 authentication succeeds, IMAP is enabled, and the server returns:

User is authenticated but not connected.

Please investigate whether there is an account-specific IMAP connectivity restriction or mailbox backend issue.

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Answer 1

I will respond in English based on your previous message. As a friendly suggestion, posting in Chinese may help your question reach a wider audience and increase the chances of receiving assistance from other community members.

Hi,

Based on what you shared, the message "User is authenticated but not connected" means that OAuth authentication is accepted, but the IMAP server cannot establish a mailbox session.

First, please check the following:

In Outlook on the web, go to Settings > Mail > Forwarding and IMAP and confirm that "Let devices and apps use IMAP is enabled".
Confirm that the clients are using:
- IMAP server: outlook.office365.com
- Port: 993
- Encryption: SSL/TLS
- Authentication: OAuth2
- Username: the complete @outlook.jp email address
Go to the account.live.com/activity page and check whether the IMAP attempts were blocked or marked as unusual
Remove the account completely from one client, revoke that client’s permission under the Microsoft account’s app permissions, and then add it again using OAuth2

For reference: POP, IMAP, and SMTP settings for Outlook.com | Microsoft Support

If the same error continues after these checks, it helps confirm an account-specific IMAP provisioning, mailbox routing, or backend connectivity problem. In this case, for further assistance, please contact Microsoft personal-account support via:

Use the Microsoft Support contact page > log in to your Microsoft account.
Enter "agent support" in the search bar and press Enter or click on Get Help.
Ignore the search results, and click on the "Contact Support" button at the bottom.
On the next page, select "Microsoft 365 and Office" and "Technical Support" from the drop-down lists, and then click on "Confirm" > "Chat with a support agent in your web browser" > enter your email address and click on "Confirm".
A chat window will open in a new tab. Wait for the operator to respond, then describe the situation to him.

I hope this helps point you in the right direction. If you have any updates or additional questions, feel free to reply back and I'll do my best to assist further.