You usually have both email tickets and 'normal' tickets in the incoming list:

Email tickets are easy to recognize:

• The title is similar to a list entry in your email program and states the sender and subject of the received email.

• In the header of the description you can see the sender address, full subject, date of receipt, etc.
• The "Email" tab is activated and gives you the option to write a reply.

If the sender has sent file attachments with their email, you will see these as attachments to the ticket.

If you want to send an email reply, activate the checkbox in the header of the "Email" tab:  and write a reply.