I'm considering creation of a web-frontend combined with a sudo-run script, so that (virtual) users may install maildrop filters in their virtual home directories. However, can that be made safe at all? - As far as I can see, maildrop filters may call any system command (like "rm -fr /var/maildirs") through command substitution. Is it possible to bring maildrop in a "safety mode" where only a limited set of directives are available?

Next: If it is somehow possible, is there a way to make maildrop do syntax checking of a filter file? - I would like to do that, so that filters with syntax errors are not installed.

If neither wish has a reasonable solution: Does someone know of solutions which somehow allow virtual users to create simple filter-rules, such as "If from X, then put in Y"? (Such as is possible with Sieve scripts.)