The Message-ID is not the mailbox item id

Message-ID is a header string

Message-ID looks like an address in angle brackets. It is an identifier the creating software put on the message. The part after @ is not the From mailbox, and it is not a domain that passed authentication, unless a different header says so.

If the header is absent, write “Message-ID not in this copy.” Do not build one from the subject.

The stored copy has its own id

The mail platform assigns an item id to the copy in a mailbox. A search, a purge, or a case note that means that stored copy needs the item id. The Message-ID can appear on more than one stored copy, for example after a user forwards the same bytes. Matching Message-ID values are a lead. They are not one mailbox item.

If you only have the header, write “mailbox item id not opened.”

What to write down

File Message-ID, the mailbox item id, and the From address, each labeled. Do not use the domain in Message-ID as the sender. Do not claim a platform search is complete when you searched only one of the two ids.

Lab: one header id and one stored copy

A lab message has Message-ID <lab-8841@mail-out.example> and From notices@lab-mail.example. The mailbox API shows item id AAMk-441 for that copy. A draft says the sender domain is mail-out.example because that is the domain in Message-ID, and uses lab-8841 as the only id in the case file.

The note quotes both ids and the From address. mail-out.example is the Message-ID domain, not the From mailbox. AAMk-441 is the stored copy. A later search for other copies can use the Message-ID as a lead and still record each item id it finds.

Message-ID: <lab-8841@mail-out.example>
mailbox item id: AAMk-441
From address: notices@lab-mail.example
write: two ids, plus the From address
not: sender domain mail-out.example