Rated 5 out of 5 stars

Very nice and efficient
but for compatibility , please make the line :
"Content-Type: multipart/related;"
the first to keep signature of mime type reachable
you can keep the line
"From: <Saved by Mozilla 5.0 (XXX)>"
in the second place

This review is for a previous version of the add-on (3.0.2.1-signed).