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Port 587 is the default mail submission port that supports all types of SMTP data transmission. May I ask port 587 is used for which function in your environmen? Please make sure the application using 587 is running in your server.
What's more, can you please provide the screenshoot of the windows firewall rule allowing 587?
Usually, we use telnet in windows to test whether a port is blocked or not. Firstly, we should Enable telnet client in Microsoft Windows operating system. For more details, please refer to:
Hope you have a nice day : )
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