POPA3D(8)

💖 POPA3D(8) — the popa3d manual, but make it cute 💖

okay bestie, gather round, because we're about to talk about popa3d — a whole Post Office Protocol server, living in section 8 of the manual (that's the System Administration girlies, iykyk 👑). this is the glow-up version. same facts, better vibes. periodt.

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✨ NAME ✨

popa3d — a Post Office Protocol (POP3) server 🦋

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✨ SYNOPSIS ✨

popa3d [-D] [-V]

that's it. that's the whole summoning ritual. no cap.

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✨ DESCRIPTION ✨

so popa3d is a Post Office Protocol version 3 (POP3) server. literally what it says on the tin. 💅

here's the tea: a POP3 server works with local mailboxes on behalf of its remote users. users can connect any time to check their mailbox and fetch whatever mail has piled up in there. the whole ✨advantage✨ of this "pull" approach is that literally any user with a basic POP3-capable mail reader program can receive mail — no full-fledged Mail Transfer Agent (MTA) required, no permanent network connection required. it's giving minimal effort, maximum mail. 🎀

⚠️ but bestie, hear me: POP3 can only be used to retrieve mail, not to send it. if you wanna send mail, that's a whole different girl — the SMTP protocol, which is what's commonly used. don't mix them up, I'm begging. 😭

to get access to a mailbox through POP3, the username must be in the password database. that's non-negotiable. and also:

• popa3d does not permit null passwords 🚫
• popa3d will refuse to serve mail for root (UID 0) users 🚫👑

like… it said no to root. iconic behavior honestly. 💀

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✨ OPTIONS ✨

• -D — Standalone server mode. in this mode, popa3d will become a daemon, accepting connections on the pop3 port (110/tcp) and forking child processes to handle them. this has lower overhead than starting popa3d from an inetd equivalent (which is what popa3d assumes by default, btw 🙈) and is thus useful on busy servers to reduce load. also, in this mode popa3d does quite a few checks to significantly reduce the impact of connection flood attacks. she's prepared. she's protected. she's that girl. 🛡️✨
• -V — print version information and exit. short, sweet, slay. 💖

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✨ COMMANDS ✨

a normal POP3 session progresses through three states: AUTHORIZATION, TRANSACTION, and UPDATE. it's a whole three-act structure, main character energy fr fr. 🌈

🌸 AUTHORIZATION state

after the TCP connection opens, the client has to authenticate itself to the server during the AUTHORIZATION state. the following commands are supported in the AUTHORIZATION state — and psst, all command names are case-insensitive 🫶

• USER name — authenticate as user name.
• PASS string — authenticate using password string.
• QUIT — quit; do not enter UPDATE state. bye bestie 👋

🦋 TRANSACTION state

when authorization is successful, the server enters the TRANSACTION state. now the client can list and retrieve messages or mark messages for deletion. the following commands are supported in the TRANSACTION state:

• DELE msg — mark message for deletion. 🗑️
• LAST — show highest message number accessed (obsolete, just so you know).
• LIST [msg] — list message number and size.
• NOOP — do nothing. literally nothing. it's the "just vibing" command. 😌
• QUIT — quit; enter UPDATE state.
• RETR msg — retrieve message.
• RSET — clear deletion marks. undo the 🗑️, we love a redemption arc.
• STAT — return total number of messages and total size.
• TOP msg n — show top n lines of message body.
• UIDL [msg] — list message number and digest.

💜 UPDATE state

when the client issues the QUIT command in the TRANSACTION state, the server enters the UPDATE state. all messages that were marked for deletion are now removed. then the server closes the connection. the end. curtains. 🎬

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✨ BUGS ✨

okay this is the part where we get real, because we have to. 😭

POP3 transmits passwords in plaintext. so if you care about the security of your individual user accounts, it should only be used either in trusted networks or tunneled over encrypted channels. that's not a suggestion, that's a boundary. 🚧

there exist extensions to the protocol that are supposed to fix this problem. popa3d does not support them yet — partly because this isn't going to fully fix the problem anyway. and in fact, APOP and the weaker defined SASL mechanisms such as CRAM-MD5 may potentially be even less secure than transmission of plaintext passwords, because of the requirement that plaintext equivalents be stored on the server. yeah. plot twist. 💀 read that twice.

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✨ AUTHORS ✨

• Solar Designer <solar at openwall.com> 💜
• this manual page is based heavily on the one Camiel Dobbelaar wrote for OpenBSD. credit where credit is due, always. 🫶

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✨ SEE ALSO ✨

• Official Internet Protocol Standard STD 53, also known as RFC 1939. 📜
• http://www.openwall.com/popa3d/

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and that's the whole page, bestie. this one's from the Openwall Project, dated 2 March 2003 — so go forth, pull your mail, tunnel your traffic, and never ever send your password into the void unencrypted. mwah 💋✨🎀