[liveoneggs]

This is how email work(ed) over smtp. When each command was sent it would get a '200'-class message (success) or 400/500-class message (failure). Sound familiar?

telnet smtp.mailserver.com 25

HELO

MAIL FROM: [e-mail]

RCPT TO: [e-mail]

DATA

blah blah blah

how's it going?

talk to you later!

.

QUIT

[1718627440]

For anyone who wants to try this against a modern server:

    openssl s_client -connect smtp.mailserver.com:smtps -crlf
    220 smtp.mailserver.com ESMTP Postfix (Debian/GNU)
    EHLO example.com
    250-smtp.mailserver.com
    250-PIPELINING
    250-SIZE 10240000
    250-VRFY
    250-ETRN
    250-AUTH PLAIN LOGIN
    250-ENHANCEDSTATUSCODES
    250-8BITMIME
    250-DSN
    250-SMTPUTF8
    250 CHUNKING

    MAIL FROM:[e-mail]
    250 2.1.0 Ok

    RCPT TO:postmaster
    250 2.1.5 Ok

    DATA
    354 End data with <CR><LF>.<CR><LF>

    Hi
    .
    250 2.0.0 Ok: queued as BADA579CCB

    QUIT
    221 2.0.0 Bye

[Telemakhos]

This brings back some fun memories from the 1990s when this was exactly how we would send prank emails.

[kstrauser]

Yep! And also, if you included a blank line and then the headers for a new email in the bottom of your message, you could tell the server, hey, here comes another email for you to process!

If you were typing into a feedback form powered by something from Matt’s Script Archive, there was about a 95% chance you could trivially get it to send out multiple emails to other parties for every one email sent to the site’s owner.

[fix4fun]

That was nice part of 1990s - many systems allow for funny things ;)

[xg15]

I like how SMTP was at least honest in calling it the "receipt to" address and not the "sender" address.

Edit: wrong.

[1718627440]

RCPT TO specifies the destination (recipient) address, the "sender" is what is written in MAIL FROM.

However what most mail programs show as sender and recipient is neither, they rather show the headers contained in the message.