Allow overwriting if admin email address.
Delete plugin options when uninstalled.
Add GPL license.
Update plugin header details.
Don't allow plugin file to be called directly.
Rework as a singleton class.
Use $plugin_slug variable.
Separate front-end and admin functionality.
Silence is golden.
Separate front-end functionality.
Update translation template file.
Text domain needs to be set on init, not plugins_loaded.
Update settings page text.
Code tidy.
Update WordPress.org plugin URI.
Remove filter support for original WP MailFrom plugin.

However, still support copying of options when first activated.
Add GitHub and Support links to plugins page.