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Editorial Team
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Asked: 2026-06-06T03:01:12+00:00

For educational purposes, I need to send an email through an SMTP server, using

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For educational purposes, I need to send an email through an SMTP server, using SMTP’s fundamental and simple rules.

I was able to do that using smtp4dev. I telnet localhost 25 and and commands are:

enter image description here

I want to do the same thing, using Gmail SMTP server. However, it requires authentication and TLS. I can’t figure out how to do that for Gmail. Here’s a screenshot of telnet smtp.gmail.com 587:

enter image description here

I searched and found many links including Wikipedia’s article about STARTTLS command. But I’m not able to use TLS and authenticate to Gmail’s SMTP server using command line (or sending commands myself in programming languages). Can anyone help?

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1 Answer

  1. Editorial Team

    to send over gmail, you need to use an encrypted connection. this is not possible with telnet alone, but you can use tools like openssl

    either connect using the starttls option in openssl to convert the plain connection to encrypted…

    openssl s_client -starttls smtp -connect smtp.gmail.com:587 -crlf -ign_eof

    or connect to a ssl sockect directly…

    openssl s_client -connect smtp.gmail.com:465 -crlf -ign_eof

    EHLO localhost

    after that, authenticate to the server using the base64 encoded username/password

    AUTH PLAIN AG15ZW1haWxAZ21haWwuY29tAG15cGFzc3dvcmQ=

    to get this from the commandline:

    echo -ne '\00user@gmail.com\00password' | base64
AHVzZXJAZ21haWwuY29tAHBhc3N3b3Jk

    then continue with “mail from:” like in your example

    example session:

    openssl s_client -connect smtp.gmail.com:465 -crlf -ign_eof
[... lots of openssl output ...]
220 mx.google.com ESMTP m46sm11546481eeh.9
EHLO localhost
250-mx.google.com at your service, [1.2.3.4]
250-SIZE 35882577
250-8BITMIME
250-AUTH LOGIN PLAIN XOAUTH
250 ENHANCEDSTATUSCODES
AUTH PLAIN AG5pY2UudHJ5QGdtYWlsLmNvbQBub2l0c25vdG15cGFzc3dvcmQ=
235 2.7.0 Accepted
MAIL FROM: <gryphius-demo@gmail.com>
250 2.1.0 OK m46sm11546481eeh.9
rcpt to: <somepoorguy@example.com>
250 2.1.5 OK m46sm11546481eeh.9
DATA
354  Go ahead m46sm11546481eeh.9
Subject: it works

yay!
.
250 2.0.0 OK 1339757532 m46sm11546481eeh.9
quit
221 2.0.0 closing connection m46sm11546481eeh.9
read:errno=0
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