Not sure if its in scope for this PR, but logically should Mailer depend on ActionView (or ActionPack for that matter)? E.g. if the app's sole purpose is to load data from DB and send out scheduled mails as plaintext, it theoretically doesn't require any routing/controller/view logic. Could there be some kind of pattern where if the library is present it leverages/enhances it, but without it some basic functionality remains working?