add email

data/email.md

@@ -0,0 +1,73 @@
+---
+title: "e-mail"
+tags: [ "data", "smtp" ]
+---
+
+This is bare-bones, original, primitive e-mail.
+
+Install `opensmtpd` (or similar), then `ncat` or `nc` or `netcat` (this mysterious cat has many names).
+
+Start the `opensmtpd` service, then use netcat to speak with the mail-daemon:
+
+
+```
+nc localhost 25
+```
+The computer should respond with code `220`, which means 'I am listening'.
+
+> 220 hex ESMTP OpenSMTPD
+
+```
+HELO gmail.com
+```
+
+You say `HELO` and say where you are coming from.
+
+
+The `smtpd` will not check, so I am going to lie to it.
+Mail servers are easily impressed, so it will be pleased to meet you.
+
+> 250 hex Hello gmail.com [::1], pleased to meet you
+
+```
+MAIL FROM: <admin@gmail.com>
+```
+
+All the mail commands start with 4 bytes, because it's easier for admins to program.
+Tell the mail daemon who you are in this format.
+
+> 250 2.0.0 Ok
+
+Then tell it who you're sending to.
+
+```
+RCPT TO: <www@dmz.rs>
+```
+
+> 250 2.1.5 Destination address valid: Recipient ok
+
+Finally, tell it that you want to send `DATA`.
+
+```
+DATA
+```
+
+> 354 Enter mail, end with "." on a line by itself
+
+```
+Subject: turn off server please
+
+very urgent
+.
+```
+
+> 250 2.0.0 73864a49 Message accepted for delivery
+
+You will find the email under `/var/spool` or `/var/mail` or similar.
+
+If unsure, just take a part of your email, like `FRAGMENT="turn off server please"`, then `grep` for it:
+
+ ```bash
+sudo grep -r $FRAGMENT /var/spool/*
+ ```
+