Suddenly "too many simultaneous mail messages"

Spike Ilacqua
Tue Feb 24 23:24:36 UTC 2004

> (I don't understand what you mean by FD_SETSIZE being unreal in any
> select() implementation that uses arrays of bits.  I've not been
> paying attention; has FreeBSD replaced the classic 4.* BSD select()
> with something like the Winsock 2.0 tactic or a wrapper for poll()?)

As far as I can tell the value of FD_SETSIZE does not necessarily
reflect the actual limit of that select(), but select() does still have
limits.  The new, recommend replacement for poll/select on FreeBSD is
kqueue().  It is supposed to be much faster that select because the file
descriptors of interest are kept by the kernel instead of being passed
back and forth from the application.  It has no limit on how many file
descriptors it can handle.

The original paper can be found at:

A tutorial:

And of course there is a man page on any FreeBSD system.

> Are you sure you want to support or allow more than 350 simultaneous
> incoming SMTP transactions per SMTP server?  If each SMTP transaction
> takes the fewer than 2 or 3 seconds it should, that amounts to more
> than 1 million mail messages per server.  Many SMTP servers hand such
> loads, but it is best to jump into them knowingly.

The server is running fine, loads are single digit, sendmail has load
and max connections per second throttles in place.  Everything seems
fine, the only problem is that DCC hits max_jobs and starts sendmail
deferring.  However the mail server handles hundreds of thousands of
messages per-day, not millions.  Maybe something else is going on?


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