Debugging a (E)SMTP/S connection

“.. The first thing to test is a TLS (aka SSL) connection. The stunnel program has special code for this, the command “stunnel -n smtp -c -r mail.example.com:25” will connect to the server via SMTP and negotiate SSL. If you use gnutls then the command “gnutls-cli -s mail.example.com -p 25” will connect to the server, […]