The server did not respond with a + response. The response was: "-ERR Logon failure: unknown user name or bad password."

Question

Hello support,

we are read email from outlook 365 using pop3 account and it's working fine from couple of years.. now suddenly get error as below while accessing from c# Service.

when i access same account from browser then it's working fine but not able to access from c# service so how username & password incorrect ?

Server did not accept user credentials
OpenPop.Pop3.Exceptions.PopServerException: The server did not respond with a + response. The response was: "-ERR Logon failure: unknown user name or bad password."
at OpenPop.Pop3.Pop3Client.IsOkResponse(String response)
at OpenPop.Pop3.Pop3Client.SendCommand(String command)
at OpenPop.Pop3.Pop3Client.AuthenticateUsingUserAndPassword(String username, String password)
at OpenPop.Pop3.Pop3Client.Authenticate(String username, String password, AuthenticationMethod authenticationMethod)
at OpenPop.Pop3.Pop3Client.Authenticate(String username, String password, AuthenticationMethod authenticationMethod)

Answer 1

Probably related to Microsoft dropping support of basic authentication. You should switch your code to oauth. See:

https://learn.microsoft.com/en-us/exchange/clients-and-mobile-in-exchange-online/deprecation-of-basic-authentication-exchange-online

Answer 2

Hey,

We just ran across this as well. MSFT is randomly selecting tenants and killing basic auth before the due date.

You can opt out but it is a rabbit hole.

https://www.reddit.com/r/sysadmin/comments/wazpl7/microsoft_just_disabled_basic_auth_for_pop3_for/

In help search for the following string to opt out.

DIAG: Enable basic auth in exo

Good luck.