Home / server / Questions / 1039943
Accepted
u123
Asked: 2020-10-25 07:54:47 +0800 CST

Send test mail using telnet via smtps (465) port

  • 772

Based on this guide I am trying to send a test email using telnet from linux

https://linuxconfig.org/send-an-email-using-telnet

but the connection immediately disconnects:

$ telnet smtp.gmail.com 465
Trying 108.177.126.108...
Connected to smtp.gmail.com.
Escape character is '^]'.
MAIL FROM: [email protected] closed by foreign host

How do I keep the connection open long enough to send my test mail?

linux smtp telnet smtps

1 Answers

  1. Best Answer

    Connections to smtp (25) start as unencrypted.
    Connections to smtps (465) start/negotiate encryption before any SMTP protocol level communication.
    You should get "SMTP greeting message" from SMTP server before sending any SMTP commands.

    Classic/standard telnet does not support encryption (ssl - Secure Socket Layer).
    You may check if your telnet program supports it.

    Linux Debian and Ubuntu

    Package telnet-ssl replaces standard telnet by telnet program with ssl support. Such telnet+ supports command line like below:

    telnet -z ssl smtp.gmail.com 465

    [2020-10-25] Debian provides telnet-ssl packages only for oldstable distributions (sid/stretch/jessie).

    One on a few alternatives is provided by gnutls-cli program from gnutls-bin Debian package.

    gnutls-cli -p 465 smtp.gmail.com
    • 5