You have chosen to encode attachment names containing non-English characters in a way that is understood by Outlook(tm) and other mail clients that do not support standard-compliant encoded attachment names. Note that KMail may create non-standard compliant messages, and consequently it is possible that your messages will not be understood by standard-compliant mail clients; so, unless you have no other choice, you should not enable this option.
Jo hawwe der foar keazen om de taheakselnammen te kodearjen dy' t net- Ingelske tekens befetsje. Outlook( tm) en oare e- postprogramma' s dy' t gjin stipe foar dizze taheakselnammen hawwe sille dizze nammen net ferwurkje kinne. Hâld der rekken mei dat KMail by it opstellen fan berjochten fan de standert ôfwikke kin, sa dat programma' s dy har wol oan de standert hâlde it net goed ferwurkje kinne. Jo moatte dizze opsje dus net oansette, of jo moatte it wier nedich ha.