I've been in the same situation, but don't think your solution is the best, maybe changing a little bit the email UI in order to let you see the common errors.

I've been in the same situation, but don't think your solution is the best, maybe changing a little bit the email UI in order to let you see the common errors. - Spell checking. - Letting you know if you haven't attached any file (in a way that you can't miss it). - About rephrasing a paragraph, maybe saving drafts before sending your email (as intellectronica says in a comment), but it should be something the user does, not the UI.