XANDIKOS-MILTER(8)

💌 XANDIKOS-MILTER(8) — the milter that reads your calendar mail so you don't have to

okay so bestie, welcome to the System Administration Utilities corner of the manual — this is XANDIKOS-MILTER, section 8, and she is serving inbound iMIP scheduling realness. let's get into it ✨

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🌸 NAME 🌸

xandikos-milter — the Postfix/Sendmail milter for inbound iMIP scheduling. like, it's the bouncer at the club door of your mail server, but for calendar invites 💅

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🦋 SYNOPSIS 🦋

xandikos-milter --lmtp-socket TARGET --listen TARGET [OPTIONS]
xandikos-milter --server-url URL --listen TARGET [OPTIONS]

two whole modes, pick one, no cap 🫶

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✨ DESCRIPTION ✨

so xandikos-milter runs a libmilter-protocol server that Postfix or Sendmail can hand each inbound message to. every single message. it's giving main character energy at the SMTP door 💖

if the message carries a valid iMIP REQUEST, REPLY or CANCEL (RFC 6047), the message gets forwarded to a running Xandikos for storage in the schedule inbox. and here's the iconic part: the message is always accepted, so normal mailbox delivery just… proceeds. no drama, no bounced mail, we move 💀

🎀 Two transports are supported. Exactly one must be configured:

okay this is the important bit — exactly one, not zero, not both. choose wisely bestie 🧚

💜 LMTP (recommended)

with --lmtp-socket, the milter forwards the raw RFC 5322 message to a running xandikos serve --imip-listen endpoint. this is symmetric with the existing iMIP LMTP listener and is the cleanest setup when the milter and Xandikos run on the same host. same host = same vibe = slay ✨

🌈 HTTP fallback

with --server-url, the extracted iTIP payload is POSTed to a Xandikos schedule-inbox URL. use this when the milter and Xandikos run on different hosts and you want HTTPS + HTTP Basic credentials between them. long distance relationship but make it secure 🔐

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⚠️ heads up: messages that carry an Auto-Submitted header other than no (RFC 3834) are skipped, to avoid loops between two Xandikos instances. no infinite loop era, we are NOT doing that 😭

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💅 OPTIONS 💅

• --lmtp-socket TARGET — LMTP endpoint of a running xandikos serve --imip-listen. pass unix:/path/to/sock for a Unix domain socket or host:port for TCP. may also be set via XANDIKOS_MILTER_LMTP_SOCKET. 🍓
• --server-url URL — schedule-inbox URL of a running Xandikos server. each iMIP payload is POSTed here as text/calendar. may also be set via XANDIKOS_MILTER_SERVER_URL. 📮
• --username USER — username for HTTP Basic authentication against --server-url. iykyk
• --password-file FILE — file containing the HTTP Basic authentication password. keep it secret, keep it safe 🤫
• --unix-socket PATH — Unix domain socket path for HTTP requests to the Xandikos server (useful when Xandikos itself listens on a Unix socket). 🧦
• --listen TARGET — listen target. pass unix:/path/to/sock for a Unix domain socket, or host:port for TCP. Postfix uses this as smtpd_milters=TARGET. may also be set via XANDIKOS_MILTER_LISTEN. 🎯
• --listen-mode MODE — file mode (octal, e.g. 660) for the Unix socket. ignored for TCP listeners.
• --listen-group GROUP — group ownership for the Unix socket. ignored for TCP listeners.

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🫶 POSTFIX CONFIGURATION 🫶

add the milter to main.cf so Postfix consults it during SMTP intake. literally just drop these in:

smtpd_milters = unix:/run/xandikos/milter.sock
non_smtpd_milters = $smtpd_milters
milter_default_action = accept

and milter_default_action = accept is the one — it ensures Postfix keeps delivering mail if the milter is unreachable. the show goes on regardless, periodt 👑

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👀 SEE ALSO 👀

• xandikos(8) — go read that one too bestie, it's the whole point 🌟

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💖 AUTHORS 💖

Jelmer Vernooij <jelmer@debian.org> — icon, legend, the moment 🎀

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and that's the whole page! this lil beauty ships as part of the xandikos project, dated May 2026 — so go forth, configure exactly one transport, and let your calendar invites find their home 💌🦋✨