Reply to email will generate new ticket ID

[Applepie2]

Hi,

In our OTRS (3.1.2), we are using the helpdesk email (helpdesk@milton-cn.com) for creating new ticket. We found that when we replied email to user and included helpdesk (helpdesk@milton-cn.com), even the original ticket is opened, OTRS will create a new ticket ID in the system. As a result, we will end up with 2 tickets for one case. it seems the OTRS did not recognize the reply is a followup to original ticket.

As in the attached screenshot, Eddy has replied to users' email and cc-ed helpdesk. Then, OTRS created its first ticket (ID: 20131126100000209).
The user then replied Eddy, and Eddy replied again. Then OTRS created another ticket (ID: 20131126100000227).

Do you have any idea?

Thanks a lot,
Rayson Wong