# WHATPORT(3905)

## NAME

port 3905 — MUPDATE (Cyrus Murder) — MUPDATE — the distributed mailbox-database protocol that keeps a Cyrus Murder mail cluster's namespace consistent.

Protocol: TCP  
IANA: mupdate

## DESCRIPTION

RFC 3656 defines the Mailbox Update protocol and IANA registered 3905 for it. In a Cyrus Murder, several IMAP/POP backends share one mailbox namespace: an MUPDATE master holds the authoritative mailbox database and makes operations on it atomic, while frontends and slaves connect to replicate it. The protocol is line-based and text-like, and a client authenticates over SASL after the server advertises its mechanisms. A listener on 3905 means a multi-server Cyrus mail cluster, not a single mail host.

## EXPOSURE

**Do not expose.** The MUPDATE master is the mail cluster's source of truth for who owns which mailbox — a strictly internal, backend-to-backend service that should be confined to the cluster's own network.

## CHECK

```sh
nc -vz TARGET 3905
```

## SEE ALSO

- spec — [RFC 3656 — The Mailbox Update (MUPDATE) Distributed Mailbox Database Protocol](https://www.rfc-editor.org/rfc/rfc3656.html) (rfc-editor.org)
- docs — [Cyrus IMAP — Murder MUPDATE details](https://www.cyrusimap.org/imap/reference/admin/murder/murder-mupdate-details.html) (cyrusimap.org)
- source — [cyrusimap/cyrus-imapd on GitHub](https://github.com/cyrusimap/cyrus-imapd) (github.com)
- iana — [IANA port registry — 3905 (mupdate)](https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml?search=3905) (iana.org)

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HTML: <https://whatport.net/3905/> · JSON: <https://whatport.net/3905.json> · full dataset: <https://whatport.net/ports.json>