Question about OpenBSD and FD_SET()

[Collin B. McClendon]

Hello,
I'm trying to put together a high volume mail server using qmail and
OpenBSD. Has anyone found what kernel paramater one would
need to get beyond the hidden file descriptor limit of 256? So far I'm
getting about 20,000 emails and hour going out with 
concurrency of 120.
Thanks,
Collin