Bug 921050 - Send email in the background.

This is sketchy or perhaps awkward.  Up at the top of the function you assign `status` into the header.  So when you manipulate `status` you are manipulating the internal state of the header.  Unlike `updateMessageBody`, `updateMessageHeader` does not have a mode of operation where it will checkpoint the current database state, so from a DB perspective this header manipulation is currently guaranteed to be the same as if you did the 'status' manipulation up above.  However, front-end slice-wise they will not see the changes here.  So that's weird.

I would propose that you do `header.sendStatus  = { stuff, i, care, about };` up top to reduce this ambiguity.