no peer certificate available

Common causes

• The server needs SNI and -servername was not given, so it aborted the handshake.
• The port does not speak TLS directly, for example a STARTTLS port such as 25 or 587 without -starttls smtp.
• No TLS version or cipher in common, so the server sent an alert or closed the connection.
• A firewall or proxy reset the connection.

How to fix it

1. Add -servername host to the command.
2. For mail ports use -starttls smtp (or imap, pop3), or connect to the implicit TLS port.
3. Read the error lines printed above "no peer certificate available"; they name the alert or failure.
4. Try -tls1_2 and -tls1_3 to see which version the server accepts.