You must name the x-header as follows: X-SP-Transact-Id.
The value associated with the header must adhere to the following:
- Maximum of 32 characters
- Only contains the characters 0-9, A-Z, a-z and the underscore ( _ )
- No spaces or other punctuation used in the value
The values of the header are not case-sensitive but they are unique. For example, 'ABC_123' and 'abc_123' are the same matching string. However, you cannot use the x-header value for any other active campaign within the organization. You can reuse an x-header if the associated transactional messages are completed or closed.
You must insert the x-header after the default (required) header elements and before the first carriage return (see red text in the example image below). If using JavaMail, note that it automatically inserts the headers in the correct location for you.
Note: Transact will not include the x-header in outbound messages; the x-header is for inbound identification only.