Disabling the extension while ses driver is active blocks access to the forum

[clarkwinkelmann]

Technically this should maybe be a core issue because nothing prevents you from entering ses in the mail driver field and get stuck as well...

Anyway mailgun and mandrill won't error until you try to use them if no configuration is set, but ses needs a region setting right from when the app boots, causing issues.

The other drivers cause Undefined index errors to appear in the log though...

We should maybe try to find a way to force the user back to a default driver when disabling the extension.