Recently I did lsof on a procmail process and it showed open file descriptors
inheritet from mpop. File descriptors should be opened with O_CLOEXEC,
SOCK_CLOEXEC or fixed afterwards with fcntl(.. FD_CLOEXEC ..).

Hi,

I don't see why this is a problem. Mpop does not start some random
program; the user has to configure it to call procmail. This is done
with popen/pclose for each mail, i.e. the procmail child process only
lives for one mail delivery. Yes it will get file descriptors, but why
is that bad? You have to trust the process anyway: it handles your mail.

There are certainly situation where you don't want to leak file
descriptors, but in this case I feel it would be a pointless
complication to set CLOEXEC everywhere.

If I miss some real problem here, please let me know.

Best regards,
Martin
(upstream maintainer)