Universal Mailer is a Mail.app plugin that solves some issues when sending emails. It removes ATT00001.htm files, it correctly formats messages with attachments and inline images, and offers an option to set the default font for outgoing messages.
When enabled, Universal Mailer is able to correctly format outgoing emails, so that even after Exchange EWS filtering they retain the original format.
The plugin runs in the background without interfering
- OS X 10.9 or later