[RCU] 8bitmime in roundcube should be disabled

[Benny Pedersen]

since it can lead to dkim spoofing

https://noxxi.de/research/breaking-dkim-on-purpose-and-by-chance.html

i am fully aware that to solve all mail user clients its not solving all 
senders not using roundcube, but it could b e a very good start

base64 use utf8 to replace it

same with quoted-printeble

if not pssoble then it needs to make mime sanitizering all, with again 
leads to even more breaks of content user sends

its it possible to change roundcube to solve it ?