You can change ticket attributes by email using variables that contain the @ symbol at the beginning of email messages.
Invalid fields and field values produce errors that are emailed back to the sender using the email error template. For more information on email templates, see Configuring email triggers and email templates.
The syntax takes the form @fieldname=. For example, the following entry clears the Due Date field:
The submitter's username, full name, or email address. The email address is used for the username and email address fields. The full name is set to the Name portion of the email address. For example, firstname.lastname@example.org.
Modify the ticket. Use one of the following: Approved, Rejected, None, or More Information Needed.
The syntax takes the form @custom_fieldname=newvalue.