I know I’m necro’ing this, but for future reference, you can with the pipes article that Takayuki linked quite easily.
You create a drop-down menu with whatever you wish to differentiate with. In your case, you may have an email address for Chicago you want to use. You simply put "Chicago|[email protected]" in. It doesn’t even display the email address, keeping it safe from spammers.
If you’re attempting to let people type their own city in, that will be more fun that you realize, as people can and will misspell their own city. However, you can simply have it as a text field (value of [City]) and as a form recipient put in "[City]@usa.com"
