Work on your email templates
Within email you have a handful of templates for newsletters, etc. They are not the most user friendly to customize. Once a user has gone to the trouble of customizing an email, provide them with a way to save it as a template. Additionally, create the functionality to revert sent messages into draft form so they can be used as a form of template- i.e. if someone else in my organization sent something, I can take it and reopen it as a draft in my email, and use all their same formatting/color choices, etc.
Garrett DeFauw commented
A template "wizard" or a template editor similar to constant contact, mailchimp or other similar services would be amazing!