I don't know, how to slove this problem. Anytime, when something is updating in some ticket, everyone from my team gets an e-mail. If one of us response on that e-mail, Jira instead of adding it to the ticket's thread, creates a new one.
"If an email message contains an issue key in its subject line and that issue key exists in your JIRA installation, the handler will add the email message content as a comment on the issue, regardless of which project the issue is in."
Thus, make sure that the emails you receive have the issuekey in the subject and mail handler is properly configured.
You must be a registered user to add a comment. If you've already registered, sign in. Otherwise, register and sign in.