Hi @Irin Sultana ,
Thank You for hiding information. I found the solution of that. It was TLS issue. I solved it.
Great to know that you've already thought of a solution and really appreciate it for your sharing!
By the way, since the Microsoft Q&A community has a policy that "The question author cannot accept their own answer. They can only accept answers by others.". and according to the scenario introduced here: Answering your own questions on Microsoft Q&A, I would make a brief summary of this thread:
I am getting this error message in my server.One of my company software is not able to send email through smtp.
I found the solution of that. It was TLS issue. I solved it.
You could click the "Accept Answer" button for this summary to close this thread, and this can make it easier for other community member's to see the useful information when reading this thread. Thanks!