IMAP4 Authentication Failure - After a while...

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IMAP4 Authentication Failure - After a while...

Markus Walter 40

Hi there, we´ve a issue with one Mailbox and connection thru IMAP.

After i restart both onpremise Server i can login with IMAP to this Mailbox. Then it takes a while and it isn´t possible. It seems that it is specific to this Mailbox.

I did a test with a new created Mailbox there isn´t an issue.

In the IMAP Logs i can find this lines:

xxxxx*****,"R=""64yd NO LOGIN failed.\r\n* BYE Connection closed. 14"";Msg=Proxy:xxx.xxxx:1993:SSL;ErrMsg=ProxyNotAuthenticated"

Any Ideas?

Best Regards Markus

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Kai Yao 37,776 Moderator

Hi @Markus Walter,

After i restart both onpremise Server i can login with IMAP to this Mailbox. Then it takes a while and it isn´t possible. It seems that it is specific to this Mailbox.I did a test with a new created Mailbox there isn´t an issue.

Are you testing in the same network? If not I would suggest switching to another network to see if it is a network issue. If this is not the case, please run the following cmdlet in Exchange Management Shell on the Exchange servers to check if it will return error messages:

Test-ImapConnectivity -ClientAccessServer Contoso12 -MailboxCredential (Get-Credential contoso\kweku)

Besides, please also have a check in application log on Exchange servers to see if you can find error or warning events which may be related.

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Markus Walter 40 Reputation points

2024-01-17T09:52:05.2433333+00:00

@Kael Yao-MSFT thanks for your hint.

It is tested within the same network. The Test-ImapConnectivity i know and i used it too for testing. So after a Exch Svr Restart the Test is successful after a while (half oder full day) it says No LOGIN failed.

What do you mean with Exchange Application Log, the IMAP4 Log ? (Path %ExchangeInstallationpath% Server\V15\Logging\IMAP4)

If yes, from there the error message in my initial post is.

Thanks so far.
Kai Yao 37,776 Reputation points Moderator

2024-01-18T01:34:53.3+00:00

What do you mean with Exchange Application Log

Sorry for not being clear in my former reply.

I meant the application log in Event Viewer.

Example:

Besides, if this issue only occurs to a specific user, would it be possible that this user has many imap clients connected to Exchange at the same time? which may cause it to reach the imap connection limit (which by default is 16).

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