3905

IANA registers UDP port 3905 as mupdate, for the Mailbox Update protocol. The available protocol specification does not establish that MUPDATE runs over UDP, so the service operating on 3905/udp is Unknown. The evidence also does not establish whether this port belongs on the public internet; its recommended exposure is therefore Unknown.

RFC 3656 describes MUPDATE as a distributed mailbox database protocol for IMAP or POP3 servers that share a mailbox namespace. It explicitly assumes a reliable data stream, such as a TCP connection. That supports describing MUPDATE’s documented transport model, but does not prove deployment on UDP or transfer the TCP evidence to UDP.

The RFC describes authenticated coordination between mailbox database participants, including master and replica roles, mailbox lookups, and streamed updates. These functions can involve sensitive mailbox names, locations, and access-control data. This context does not establish observed use, prevalence, or malware activity on 3905/udp.

Registered service

IANA lists mupdate (Mailbox Update protocol) for UDP port 3905; this is an assignment, not evidence of a running UDP service.

UDP protocol status

Unknown. RFC 3656 specifies MUPDATE over a reliable data stream such as TCP; it does not establish MUPDATE over UDP.

Exposure

Unknown. The evidence does not establish the intended audience for a UDP service on this port.

Analyst note

Do not treat the registered name as proof that MUPDATE traffic is present on UDP.

IANA service name

mupdate — Mailbox Update (MUPDATE) protocol [Confirmed] — https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.csv

Documented MUPDATE use

Distributed mailbox database protocol for IMAP or POP3 servers sharing a mailbox namespace [Confirmed] — https://www.rfc-editor.org/rfc/rfc3656.txt

Documented transport

Reliable data stream, such as TCP; UDP operation is not established [Confirmed] — https://www.rfc-editor.org/rfc/rfc3656.txt