https://www.sslforfree.com/
https://gethttpsforfree.com/ ; requires that you register you public key for the email.
Verify SSL:
https://www.ssllabs.com/
If you want to know DKIM (the public key to your domain or email), use this site:
https://protodave.com/tools/dkim-key-checker/
Use "default" under the selector.
You may find public key for any domain here. Usually, email public key is same as domain public key.
https://www.sslshopper.com/ssl-converter.html for converting code signing certification .pfx file generation.