Reply threading and the ticket reference tag

Email replies are kept on the right ticket using a reference tag in the subject line.

The reference tag

Outbound ticket emails include the ticket number, and threading looks for a tag of the form [T-NNNNN] in the inbound subject (the match is case-insensitive). The number inside is normalised to the canonical five-digit ticket number, e.g. [T-123] resolves to T-00123.

How a match is threaded

When the tag matches an existing ticket that is still open — specifically status open, in_progress, waiting_customer, or waiting_third_party — the message is added as a client-visible reply (with no author, marking it as from the client). The system then:

• Adds a system note recording that the client replied via email and from which address.
• Sets the ticket's awaiting agent reply flag so it surfaces in the owner's Needs Reply view.

When no match is found

If there's no tag, or the referenced ticket isn't in an open state, the email is not threaded — a brand-new ticket is created instead. Keep the tag intact in the subject so replies land on the original ticket.