Sure, you can set up your own ticket sources. This can be set up from the company profile, from the lower left-hand section. First select the settings cog then from there select Company.
Once in the companies settings in the left-hand pane, you will see the option for Ticket Sources.
Note: Only administrators on your Teamwork Desk account can add/edit or delete ticket sources.
Email is the Source selected when a ticket was created from the automated forward.
Email (manual) can be selected to indicate that the ticket was created manually and that it didn't arrive by the automated forward. It could also indicate if the ticket was manually forwarded.
Docs is for tickets created from the "Submit a Request" button on your Help Docs Site.
Phone can be used for tickets that were created on behalf of the customer as a result of a Phone Call.