Port 628QMQP (Quick Mail Queuing Protocol)

Qmail's Quick Mail Queuing Protocol for submitting messages directly to a mail queue.

transport: tcp · udp
in transit: cleartext
assignment: official
risk: 5/10
lookups: 0

also known as Quick Mail Queuing Protocol, qmail-qmqpd

Technical Details

what runs on :628

QMQP is a qmail-specific mail injection protocol, normally carried over a TCP stream and using qmail's netstring-style framing for the envelope and message content. The base protocol provides no TLS negotiation or client authentication; deployments rely on network-level access controls and the qmail service configuration. Related qmail protocols include SMTP on port 25 and QMTP on port 209.

Security Information

exposure of :628

risk score

5/ 10caution

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

email averages 3.8 across 44 ports — this one sits 1.2 above.

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

An exposed QMQP service can let an unauthenticated or insufficiently restricted peer inject mail into the local queue, enabling spam relay, queue abuse, and cleartext disclosure of message contents. It should generally be limited to explicitly trusted hosts and not placed directly on the public Internet.

Record

iana registry entry

port: :628
service: QMQP (Quick Mail Queuing Protocol)
transport: TCPUDP
encryption: cleartext
assignment: iana registered
risk: 5/10caution
category: Email
usage: QMQP is used by qmail installations to submit messages directly to a queue manager, usually through the qmail-qmqpd service on TCP port 628. It is typically restricted to trusted hosts rather than exposed as a general-purpose Internet mail submission service; IANA lists the assignment for both TCP and UDP.
lookups: 0rank 994
added: 2026-08-24
updated: 2026-08-24
references: IANA service name registry — port 628

Something wrong?

This record is maintained by the engineers who use port 628. 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 2026-08-24.

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 44 in email →

the 8 most looked-up other ports in email — 44 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 :628QMQP (Quick Mail Queuing Protocol)

Technical Details

Security Information

Related Ports

Port 628QMQP (Quick Mail Queuing Protocol)