Allow search by any header in email, add search to Queue & Held

[dragoangel]

What point of X-Postal-MsgID if you can't search by it? 😊
I think postal can easy search by any header[key=value] but it not support this 😢

[willpower232]

I've always hoped some search improvements were possible but haven't had an opportunity to see if the database would or would not help in its current state.