SMTP

SMTP is a networking protocol for mail transfer.

Troubleshooting

TLS

1. Prepare encoded strings for your mail username and password

echo -ne "mail@example.net" | base64

1. Connect to mail server

openssl s_client -starttls smtp -connect smtp.example.com:587

1. Send HELO

EHLO

1. Authenticate

AUTH LOGIN
<your-encoded-username>
<your-encoded-password>

If that's successful the mail server should return 235 2.7.0 Authentication successful.