I'd suggest to create an action rule. I did some testing about this procedure and it works like a gem. Go to Setup > Processes > Action Rules and create one. For the category and action, see below screenshots.
Created a subject that contains a keyword.
Went to actions tab and selected modify ticket and edited it to assign to a specific request type. Saved the action rule.
Created a ticket through email and the action rule worked fine and assigned it to the request type specified in the rule.
Let me know if we're on the same page.
Wouldn't that affect ALL incoming e-mails? I already have incoming emails set those tickets in a general category and I don't want that to change. To be more specific; I'm setting up a web filter that will have a block page with the WHD email link to create a ticket, (assuming the block is incorrect and needs whitelisted). I want emails from that web filter block link to be categorized as 'web filter' within WHD.
As far as WHD sees it, this would just be another email generated ticket so I believe the only way to categorize it differently is to edit the text in the incoming email's subject line, but I don't know what the text needs to be for WHD to categorize it for the web filter. I imagine this should be similar to how clients can close tickets by sending an e-mail, with "Ticket:### Status:Closed" in the subject line.
No. The criteria on your action rule says to only run the rule when a "Subject" contains "Toner" (in this case). The action rule will evaluate every message, but only alter the ones that contain the criteria.