Link emails to a ticket

Link emails to a ticket

I need to know the ID to link an email to a ticket. For example, I need to send an email to a supplier, but it should automatically link to a ServiceDesk ticket. I tried including the ticket number in the subject line, but it does not link (a new ticket is created). I also tried including the ticket number in the body of the email, but it still does not link.

Thank you very much for your help.

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