Security Scan/Search engines
https://www.censys.io
Censys collects data on hosts and websites through daily ZMap and ZGrab scans of the IPv4 address space, in turn maintaining a database of how hosts and websites are configured
Mailserver TLS Tests:
https://de.ssl-tools.net/mailservers/
http://www.checktls.com/
Webserver TLS SSL Tests
https://www.ssllabs.com/ssltest/
Allows deep analysis of the configuration of any SSL web server on the public Internet.
Webserver Security Header Tests
https://securityheaders.io
Owasp
https://www.owasp.org/index.php/List_of_useful_HTTP_headers