MT message structure

IN ONE LINE

An everyday analogy: an MT message is a letter written on a strict pre-printed form.

The envelope says who sent it, who must receive it, and how urgent it is — that is the job of the headers.

Inside, the form has numbered boxes, and every box has one fixed meaning: box 20 is always your reference, box 32A is always the date, currency, and amount.

Stapled to the back is a slip the postal system uses for its own checks — the trailers.

Because everyone fills in the same boxes the same way, a bank on one side of the world can read a form filled in on the other side without ever phoning to ask what a field means.

That rigid sameness is the whole point of a message standard.

WHAT IT ACTUALLY IS

An MT (message type) is identified by three digits — MT103, MT202, MT940 — where the first digit is the category: 1 for customer payments, 2 for financial institution transfers, 9 for cash management.

Every MT message is built from up to five blocks.

Block 1, the basic header, identifies the sender and the session.

Block 2, the application header, carries the message type, the receiver, and the priority.

Block 3, the optional user header, carries service data — most importantly field 121, the UETR, a unique end-to-end transaction reference that lets one payment be tracked across every bank it touches.

Block 4 is the text: the business content, arranged as numbered fields.

Block 5 holds trailers used for control and authentication.

HOW IT WORKS

Practitioners rarely read whole messages; they read the fields that matter for the problem in front of them.

Block 2 answers "what is this and which direction did it travel" — an input message is one your institution sent, an output message is one it received.

Field 20 in block 4 is the sender's reference, the key that queries, investigations, and returns are built around; banks downstream quote it in their own related-reference fields, chaining the journey together.

The UETR does the same job network-wide and is what tracking tools query.

When a message violates format rules, the network refuses it and the sender sees a negative acknowledgement — so a surprising share of exception work happens before a counterparty ever sees the payment.

Screening and repair systems are, underneath, parsers of these same blocks and tags.

THE WORDS

MT message

A message in SWIFT's legacy Message Type format: numbered categories and tag-based fields, exchanged over the FIN service.

UETR

A unique reference in UUID format that stays with a payment across every leg, so all banks in the chain can track the same transaction.

READ FIRST

• The SWIFT network and BICs

CONNECTED TO

• MT103 MT103 — Single Customer Credit Transfer
• CHECKPOINT SWIFT MT structure checkpoint

SOURCES

• Swift Standards MT (annual standards releases) — Swift
• Payments Signal editorial teaching models — Payments Signal