Error 530 5.7.0 must issue a STARTTLS command first Exchange 2016

ali khoshbin 1 Reputation point

Dear Colleagues,
I am acting as a consultant for a company. They have exchange 2016 installed and a mail relay with IIS 7.5 installed. They have problem with only 1 domain with below error:
Error 530 5.7.0 must issue a STARTTLS command first
I tried to telnet to that domain, but as long as I enter mail from:<info@keyman .com> I got the above error.
The other side is also using exchange 2016.
Do you have any suggestions as what steps should be taken to solve the issue?
Thanks in advance

Exchange Server Management
Exchange Server Management
Exchange Server: A family of Microsoft client/server messaging and collaboration software.Management: The act or process of organizing, handling, directing or controlling something.
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  1. ali khoshbin 1 Reputation point

    HI KaelYao
    As I mentioned, the company is only using the mail relay with SMTP service installed on IIS 7.5.
    There is no exchange server installed, so I could not execute that command.
    Is there any suggestions?
    Thanks for your followup