This message type is used by financial institutions, with their own offices, and/or with other financial institutions with which they have established bilateral agreements.
It is used as an envelope for a specified message included in it.
It allows for the definition of a unique format for which another message type is not available or applicable.
It also allows financial institutions to use message types which are awaiting live implementation on the SWIFT system.
| Status | Tag | Field Name | Content/Options | No. |
| M | 20 | Transaction Reference Number | 16x | 1 |
| M | 12 | Sub-Message Type | 3!n | 2 |
| M | 77E | Proprietary Message | 73x [n*78x] |
3 |
There are no network validated rules for this message type.
When assigning a category to this message, eg, 198 versus 498, the users should select the category that, at a general level, encompasses the business purpose of the message.
The sub-message type number agreed to by the users of a specific proprietary message, or the message type assigned to a message format being used before implementation, shall be identified in field 12 of the message being transmitted.