46,176 questions
![](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
server unavailable.21 error when connect to outlook using pop
![](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(96, 89%, 19%)' cx='32' cy='32' r='32' /%3E%3Ctext x='50%25' y='55%25' dominant-baseline='middle' text-anchor='middle' fill='%23FFF' %3EIT%3C/text%3E%3C/svg%3E)
Ivan Tsai
50
Reputation points
My program connects to outlook using pop and was running properly before this morning.
It crashed with error message "server unavailable.21" this morning
Community Center Not monitored
{count} votes
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Carolyn Parker 0 Reputation points2023-06-09T23:13:03.94+00:00 I have the same problem on both my home Windows 10 computers. Just started today. Has anyone received an answer/fix for this problem?
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Paulo de la Rosa 0 Reputation points2023-06-09T23:59:21.0366667+00:00 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.
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![](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)
Miloš Tomin 10 Reputation points2023-06-10T00:38:58.5333333+00:00 Same problem Using Thunderbird email client.
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Test Tech 5 Reputation points2023-06-10T01:02:26.9633333+00:00 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.
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![](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)
Viktor Iakubchak 5 Reputation points2023-06-10T07:55:08.7366667+00:00 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
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Paulo de la Rosa 0 Reputation points
2023-06-10T11:38:53.3466667+00:00 any response from microsoft?
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Miloš Tomin 10 Reputation points
2023-06-10T18:01:16.5633333+00:00 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.
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Viktor Iakubchak 5 Reputation points
2023-06-12T06:17:12.2433333+00:00 works from yesterday evening (in my case)
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Paulo de la Rosa 0 Reputation points
2023-06-12T11:00:43.19+00:00 In my case works too. Thanks to those who fixed it.
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Viktor Iakubchak 5 Reputation points
2024-11-25T15:28:24.6266667+00:00 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
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