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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: asdasd@asd.Connection closed by foreign host

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

AnFi
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u123
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1 Answers1

5

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
AnFi
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