> Subject: Testing åøæ
> 
> Becomes
> Subject: IKT sak =?UNKNOWN?B?KDYwKTo=?= Testing =?UNKNOWN?B?5fjm?=
> 
> config:
> Use Email Subject = IKT sak ($message id): $Tittel

You could put the encoding there manually:

Use Email Subject = =?ISO-8859-1?Q?IKT sak ($message id): $Tittel?=

would this work?