Here is a problem, which I can reproduce:
EmailOutputEncoding is ISO-8859-1
User “lueck” with email "firstname.lastname@example.org" and Realname “Sebastian
Lück” produces in From-headers originated by RT 3.0.2pre6:
The ISO-encoded string should not span the first part of the emailadress.
At most two MUAs I use (Mulberry, mutt) cannot decode this, and I think -
but I am not sure - it is illegal.