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My program connects to outlook using pop and was running properly before this morning.
It crashed with error message "server unavailable.21" this morning
![](data:image/svg+xml, %3Csvg xmlns='http://www.w3.org/2000/svg' height='64' class='font-weight-bold' style='font: 600 30.11764705882353px "SegoeUI", Arial' width='64'%3E%3Ccircle fill='hsl(41.6, 52%, 14%)' cx='32' cy='32' r='32' /%3E%3Ctext x='50%25' y='55%25' dominant-baseline='middle' text-anchor='middle' fill='%23FFF' %3ECP%3C/text%3E%3C/svg%3E)
I have the same problem on both my home Windows 10 computers. Just started today. Has anyone received an answer/fix for this problem?
![](data:image/svg+xml, %3Csvg xmlns='http://www.w3.org/2000/svg' height='64' class='font-weight-bold' style='font: 600 30.11764705882353px "SegoeUI", Arial' width='64'%3E%3Ccircle fill='hsl(28.799999999999997, 16%, 12%)' cx='32' cy='32' r='32' /%3E%3Ctext x='50%25' y='55%25' dominant-baseline='middle' text-anchor='middle' fill='%23FFF' %3EPD%3C/text%3E%3C/svg%3E)
I started having this problem just today. I'm using windows 7. I'd checked the account settings in thunderbird and it's ok, but every time I've tried, it has given the same error.
Also, I've set my outlook account to allow devices and programs to use POP.
I'll appreciate any help about this issue.
![](data:image/svg+xml, %3Csvg xmlns='http://www.w3.org/2000/svg' height='64' class='font-weight-bold' style='font: 600 30.11764705882353px "SegoeUI", Arial' width='64'%3E%3Ccircle fill='hsl(166.4, 32%, 26%)' cx='32' cy='32' r='32' /%3E%3Ctext x='50%25' y='55%25' dominant-baseline='middle' text-anchor='middle' fill='%23FFF' %3EMT%3C/text%3E%3C/svg%3E)
Same problem Using Thunderbird email client.
![](data:image/svg+xml, %3Csvg xmlns='http://www.w3.org/2000/svg' height='64' class='font-weight-bold' style='font: 600 30.11764705882353px "SegoeUI", Arial' width='64'%3E%3Ccircle fill='hsl(28.799999999999997, 17%, 12%)' cx='32' cy='32' r='32' /%3E%3Ctext x='50%25' y='55%25' dominant-baseline='middle' text-anchor='middle' fill='%23FFF' %3ETT%3C/text%3E%3C/svg%3E)
Same here. POP3 OAuth2.0. Tried one 3rd party app and also Thunderbird. We tried creating new mailbox for testing, it could authenticate the first few times, but later, it get the same error "Server Unavailable. 21". Please fix.
![](data:image/svg+xml, %3Csvg xmlns='http://www.w3.org/2000/svg' height='64' class='font-weight-bold' style='font: 600 30.11764705882353px "SegoeUI", Arial' width='64'%3E%3Ccircle fill='hsl(16, 42%, 11%)' cx='32' cy='32' r='32' /%3E%3Ctext x='50%25' y='55%25' dominant-baseline='middle' text-anchor='middle' fill='%23FFF' %3EVI%3C/text%3E%3C/svg%3E)
same:
Log onto incoming mail server (POP3): Your incoming (POP3) email server has reported an internal error. If you continue to receive this message, contact your server administrator or Internet service provider (ISP). The server responded: -ERR Server Unavailable. 21
any response from microsoft?
The new development is that a few messages get pulled down to Thunderbird, but they are old messages from a month ago and only about 4 to 5. Then it glitches again and no new messages are downloaded.
works from yesterday evening (in my case)
In my case works too. Thanks to those who fixed it.
FYI
Modern Authentication Methods now needed to continue syncing Outlook Email in non-Microsoft email apps. Microsoft has indeed removed support for POP3 and PST files for Outlook.comaccounts as of September 16, 2024, due to security reasons. They now require Modern Authentication for accessing email accounts
https://support.microsoft.com/en-us/office/modern-authentication-methods-now-needed-to-continue-syncing-outlook-email-in-non-microsoft-email-apps-c5d65390-9676-4763-b41f-d7986499a90d
![](data:image/svg+xml, %3Csvg xmlns='http://www.w3.org/2000/svg' height='64' class='font-weight-bold' style='font: 600 30.11764705882353px "SegoeUI", Arial' width='64'%3E%3Ccircle fill='hsl(83.2, 20%, 18%)' cx='32' cy='32' r='32' /%3E%3Ctext x='50%25' y='55%25' dominant-baseline='middle' text-anchor='middle' fill='%23FFF' %3EIA%3C/text%3E%3C/svg%3E)
The same problem "Error 21 Server Unavailable" with Thunderbird client. All worked perfectly until some changes from Microsoft was made. Please help people to resolve a problem, no answer from Microsoft support