Roundcube ATT####.dat in Outlook with diacritical characters

When you get reports that some people get e-mails from Roundcube that have ATT####.dat attachments, check if they’re using Microsoft programs, especially Outlook Express. They don’t (of course) implement the most recent RFCs, so if attachment name contains diacritical characters (such as Polish ą, ć, ś, etc.) it gets corrupted. When using Roundcube, the solution is quite simple — search the main config file for „mime_param_folding” and change its value from 0 to 1.