Review for Outgoing Message Format by gamebouille
Rated 5 out of 5 stars
Oh thanks !
It's unbelievable that thunderbird doesn't have this feature build-in.
My problem was that I must send email in HTML format because the mail server from my company reformat email if it's not in HTMLformat... and add weird spacing in the original email.
Since I can force HTML format for every email with this add on, I don't have this problem anymore.
To create your own collections, you must have a Mozilla Add-ons account.