How to use OpenSSL to check certificate used

Download OpenSSL from: https://www.openssl.org/source/ 

(Windows version from: https://slproweb.com/products/Win32OpenSSL.html)

Install and open it from command prompt.

Now run the command

openssl s_client -connect host.example.com:port

where port is one of the following

993 is for IMAPs

443 is for HTTPS

465 is for SMTPs

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