Looking for logging into the Microsoft Smtp User site and are not getting the correct working link for it? In such a case, you can use the links given here by searching your desired login page in the search box. If the page is present on our website then you will get all the links related to the Microsoft Smtp User site. After that you can login as usual with your login credentials.
https://blogs.technet.microsoft.com/mikelee/2018/09/22/is-smtp-auth-really-working/
https://docs.microsoft.com/de-de/exchange/clients/pop3-and-imap4/configure-authenticated-smtp
https://social.technet.microsoft.com/Forums/exchange/en-US/1c721f0d-25f1-4228-a363-3f524830f380/how-to-open-smtp-for-authenticated-relay?forum=exchangesvrsecuremessaging
https://social.technet.microsoft.com/Forums/en-US/8b4b5ea4-f51f-48b2-81cc-6d102e43ccbd/does-smtp-authorization-needs-user-with-mailbox-or-ad-account-only?forum=exchangesvrsecuremessaginglegacy
https://blogs.technet.microsoft.com/exchange/2018/04/20/changes-coming-to-the-smtp-authenticated-submission-client-protocol/
https://social.technet.microsoft.com/Forums/en-US/dabdd759-d395-48fc-b3c4-c610eba46702/exchange-server-smtp-authentication?forum=exchangesvradminlegacy
https://social.technet.microsoft.com/Forums/exchange/en-US/68a987be-bbd2-4d86-a5b4-f3addc81d305/cant-smtp-send-with-credentials-from-users-without-mailboxes?forum=Exch2016MFSM
https://social.technet.microsoft.com/Forums/ie/en-US/f0725a29-4ab9-4ba1-807d-83b5981d761a/smtp-auth-login-attempts-causing-ad-user-account-lockouts?forum=exchange2010
https://docs.microsoft.com/de-de/exchange/mail-flow/test-smtp-with-telnet
https://social.technet.microsoft.com/Forums/lync/en-US/3b6a1c2e-4fc7-48e2-80f5-9c433c61bec9/requiring-smtp-authentication?forum=exchangesvrsecuremessaginglegacy
https://docs.microsoft.com/de-de/dotnet/api/system.net.mail.smtpclient.usedefaultcredentials
https://social.technet.microsoft.com/Forums/exchange/en-US/08ba2bcf-d9f2-4371-93b1-e11fcd89c8b1/exchange-smtp-auth-login-doesnt-work?forum=exchangesvrsecuremessaginglegacy
https://social.technet.microsoft.com/Forums/en-US/afe2b491-1231-48a8-a073-d4251de9f4fe/exchange-2007-smtp-authentication-how-to-see-what-user-is-trying-to-authenticate?forum=exchangesvrsecuremessaginglegacy