Port 3905Cyrus MUPDATE (Mailbox Update Protocol)

Mailbox location and metadata updates between Cyrus IMAP Murder servers.

transport: tcp · udp
in transit: cleartext
assignment: official
risk: 3/10
lookups: 0

also known as Mailbox Update Protocol, Cyrus Murder MUPDATE

Technical Details

what runs on :3905

MUPDATE is a command-oriented mailbox update protocol used by Cyrus IMAP Murder. It normally runs over a persistent TCP connection on port 3905, with command/response exchanges used to query and update the mailbox-location database; the IANA assignment also lists UDP. It is distinct from client-facing IMAP and SMTP service ports, and is generally deployed only between trusted Cyrus components.

Security Information

exposure of :3905

risk score

3/ 10caution

worth attention. how exposed you are depends on configuration — don't leave it reachable from the internet without a reason.

email averages 3.4 across 52 ports — this one sits 0.4 below.

in transit

cleartext

credentials and payloads are readable by anyone on path

assignment

official

registered with iana for this service — scanners fingerprint it by number

reachable over

tcp · udp

udp is connectionless — source addresses are trivially spoofed and it is a reflection favourite

security overview

Port 3905 should normally be restricted to the Cyrus cluster because it exposes an internal mailbox-location management service rather than a public mail endpoint. Traffic is not encrypted by default, so deployments should rely on network isolation and the protocol's configured authentication or TLS support where available; internet exposure can enable probing and attempted unauthorized cluster operations.

Record

iana registry entry

port: :3905
service: Cyrus MUPDATE (Mailbox Update Protocol)
transport: TCPUDP
encryption: cleartext
assignment: iana registered
risk: 3/10caution
category: Email Network Services
usage: MUPDATE is used by Cyrus IMAP Murder deployments to maintain and distribute mailbox location information between frontend and backend servers. Engineers usually encounter it only on internal Cyrus cluster networks, not as a public mail service.
lookups: 0rank 994
added: 2026-09-08
updated: 2026-09-08
references: IANA service name registry — port 3905
RFC 3656

Something wrong?

This record is maintained by the engineers who use port 3905. Every field on it is editable — change what's wrong, say how you know, and a reviewer publishes it, usually within a minute. Last touched 2026-09-08.

01edit any field on a page of its own
02a model checks it for accuracy and spam
03clean and confident goes live immediately

edit this record →back to the registry

Related Ports

all 52 in email →

the 8 most looked-up other ports in email — 52 ports carry that label.

port	service	proto	category	risk	views
:143	IMAP	TCPUDP	Email	caution	20.7k
:995	POP3S	TCPtls	Email	caution	18.8k
:109	POP2	TCP	Email	caution	17.9k
:2096	cPanel SSL Webmail	TCPtls	Web Services	safe	17.4k
:110	POP3	TCP	Email	caution	15.5k
:993	IMAPS	TCPtls	Email	caution	14.5k
:1352	Lotus Notes RPC	TCP	Email	caution	12.3k
:24	Private Mail	TCPUDP	Email	caution	11.7k

risk mix of the 8 listed

safe13%
caution88%

3 of 8 encrypted

Port :3905Cyrus MUPDATE (Mailbox Update Protocol)

Technical Details

Security Information

Related Ports

Port 3905Cyrus MUPDATE (Mailbox Update Protocol)