When encrypting the data exchanged with the mail server, you will need to get the ‘public key’ of the mail server, so that only the mail server is able to decrypt the email using the secret ‘private key’. The public key should be freely available as a .cer file, but often you will need to contact the mail server to get it. One way is to use a free tool called ‘OpenSSL’, which you can download here:
http://slproweb.com/products/Win32OpenSSL.html
After installation you run it via DOS session. In the DOS session you change the directory to the bin directory containing the OpenSSL installation. This can e.g. be C:\OpenSSL-win64\bin:
After executing ‘openssl’ you will get an OpenSSL prompt like above.
For getting the SSL certificate from e.g. Gmail you should run this command:
s_client -connect smtp.gmail.com:465
This command will get the TLS certificate:
s_client -connect smtp.gmail.com:587 -starttls smtp
In the DOS Session you will see a lot of data and the certificate starting with
-----BEGIN CERTIFICATE----- and ending with -----END CERTIFICATE-----
like below:
You should now copy the text starting with (and including) ---- BEGIN CERTIFICATE---- until (and including) -----END CERTIFICATE----- and paste it into Notepad. Now save the file in Notepad as a certificate file with the extension .cer. This file contains the certificate, that we would like to import in the section below.
