SMTP using netcat

2026-01-20 smtp netcat telnet

Commands don’t need to be upper case.
The mail from: address needs to be in RFC format. Some servers will accept anything though.
Some servers (Gmail) require data headers such as From:.
Starting netcat with -C sends CRLF line feeds which may be required.

$ nc smtp.example.com 25
220 smtp.toennjes.dev ESMTP Postfix (Debian)

EHLO marvin.yelnah.org

MAIL FROM: <felix@userspace.com.au>
RCPT TO: <recipient@example.com>
DATA
Subject: test01
From: felix@userspace.com.au
To: recipient@example.com

Blah blah
.
QUIT