OpenSSL Builder
Mail TLS Test Commands
Build a verified SMTP or IMAP TLS diagnostic command.
Usage guide & examples
1. Choose the connection mode. SSL/TLS encrypts immediately after TCP connection (usually SMTP 465 / IMAP 993). STARTTLS upgrades an initial protocol connection (usually SMTP 587 / IMAP 143). Defaults are suggestions; server settings may differ.
2. For a plaintext capability check, run the example below, then inspect STARTTLS in the reply. Telnet cannot negotiate TLS; never send credentials here. Port 25 is mainly server-to-server SMTP. An immediate TLS port cannot be tested with this Telnet flow.
3. To test encryption and certificates, generate an OpenSSL command below. Check installation with openssl version. If unavailable, install through your OS package manager / IT administrator. Telnet may also require installation. OpenSSL is a TLS-capable client.
Console flow / input example
telnet mail.example.com 587 EHLO client.example.com 250-STARTTLS QUIT
Processed locally. No input is uploaded or stored.
Scope
Generated text only. Nothing is executed or connected from this page.
Requires OpenSSL s_client on your machine and a working CA trust store. Certificate verification is enabled; check server replies before sending commands.
Result
Where do I use this result?
Run OpenSSL in your terminal to check TLS, the certificate and STARTTLS negotiation. First check installation with openssl version. A trusted CA store is required.
OpenSSL Builder details