The overhead of the try block is very low, so if no exception is thrown then there should be no noticeable penalty. The main overhead that occurs when an exception is thrown is the stack walk that takes place looking for a handler - since you are caching the exception so close to the source, I doubt there will be much of a performance issue. Ideally though you would be able to validate your inputs properly beforehand, but email validation is fairly complicated so it may well not be worth it in this case.
