How do email replies get appended to existing tickets?

Email replies will be appended to existing tickets based on whether they pass a series of checks. The checks are performed in the following order:

1. First, Kayako checks for the ticket ID in subject with the correct format (i.e. [#Ticket ID:]. If found, the reply gets appended to the existing ticket.
2. Second, the Kayako searches for the ticket ID in the body of the reply.
   NOTE: This check is only performed if you've enabled the Search for ticket ID in email body option.
3. Finally, Kayako looks for a ':' with the existing ticket subject from the same user. If it finds a match, then the reply gets appended.

For any discrepancies when replies are added to existing tickets, you can look for the attributes above in the parser logs for those tickets.