Email threading

A customer's reply joins the existing ticket rather than opening a new one, using the standard reply headers — including the whole References chain, so threads connect even when a mail client changes the subject.

• When the headers are missing (some mail clients drop them, or the CSM edited and sent a draft from Gmail), a reply whose subject starts with "Re:" or "Fwd:" (or AW:, SV: and other languages' versions; ticket tags like [CL-0042] are ignored) joins the email ticket on the same account with the exact same subject from the last 60 days; failing that, a near-identical subject (85%+ similar) — but only when one ticket is clearly the best match, and only when the sender's email domain is already on that ticket, so one customer's "Re: Invoice" never joins another's. A fresh subject always opens its own ticket.
• Tickets merged by hand in Clynto (Merge into) or in Freshdesk keep threading: a later reply to either ticket lands on the one that was kept.
• This works for conversations too: a customer replying to an email Clynto sent or drafted lands on that conversation ticket.
• A reply to a closed ticket reopens it.
• Processing the same message twice never duplicates it.