backport #14318 to 4-1 .
I am 95% that this fixed the mailer issue on travis.
travis is now failing randomly for another reason:
ArgumentError: key cannot be blank
So we should backport this to 4-1-stable. cc @pixeltrix
Make sure we clean preview_interceptors
We should make sure we clean preview_interceptors after each test so they dont leaky to the next test
With current master I personally still have this random failure (see this gist). :-(
Anyway seems 👍 to have this in