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I know somebody here will say that this is a duplicate of some thread but, I dont get a clear answers from those thread and also not found anything that works as of this writing.

We just encounterred the 401 unauthorized on our API that uses Microsoft.Exchange.WebServices.Data's codes for sending automated emails that was working before

I checked the shared mailbox we used if its credential thats causing the issue however, it seems to not be the issue as its still valid

Are there any changes or updates done relating to this?

Are there any new approach to make it work again?

aj go
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  • It may be a TLS issue. Are you using HTTP or HTTPS? It may be that you are using HTTP and the server got changed to require TLS (HTTPS). – jdweng May 25 '21 at 11:57
  • I'm using HTTPS in the app. The link of exchange mailer is also in https protocol – aj go May 25 '21 at 13:03
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    It looks like the connection is completing. Using TLS you would not get a response from server (401). See if following helps : https://learn.microsoft.com/en-us/answers/questions/27804/exchange-web-service-the-remote-server-returned-an.html?force_isolation=true – jdweng May 25 '21 at 13:17
  • Is it possible to a shared mailbox email have mfa? I think no setting about mfa on it – aj go May 25 '21 at 16:10
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    There could be three levels 1) SMTP which normally uses for security port 465 or 487 2) Then you have the Network Credentials 3) And then you may have a firewall. Normally Outlook Server will have a Proxy Server that handles the credentials. – jdweng May 25 '21 at 16:38
  • This is really frustrating. I dont have any access to configure the MFA setting of the shared mailbox I am using which is one factor that causes this issue. Its a custom shared mailbox btw – aj go May 28 '21 at 02:21
  • The SMTP connection requires the From address and the Credentials to to be from the same account. I don't know what that means with a shared email account. I believe a shared email account mean that multiple people can read the email, but not sure what happens for sending emails. Read following : https://techcommunity.microsoft.com/t5/exchange/exchange-online-shared-mailbox-smtp-and-imap/m-p/85783?force_isolation=true – jdweng May 28 '21 at 09:37

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