Use Telnet to test SMTP communication on Exchange servers ...
docs.microsoft.com › test-smtp-with-telnetAug 20, 2021 · Did you know that, instead of using Telnet to test SMTP connectivity, you can use the Microsoft Remote Connectivity Analyzer at https://testconnectivity.microsoft.com/? With the Remote Connectivity Analyzer, you can choose the connectivity test you want to do, in this case Inbound SMTP Email, and follow the instructions shown. It'll step you through the information you need to enter, run the test for you, and then give you the results.