I found that even this wasn't lightweight enough on the filter server I'm adminning, so I wrote a microprogram to use the load average instead. Ideally, this should be hacked into sendmail itself in some way; I'm not going there myself. I *might* poke it into procmail if I get inspired some day.
Unless I'm misunderstanding what your procmail recipes are doing, it's *alread* been hacked into Sendmail.
From a sendmail.cf file I've got lying around:
# load average at which we just queue messages
#O QueueLA=8
# load average at which we refuse connections
#O RefuseLA=12
# load average at which we delay connections; 0 means no limit #O DelayLA=0
The "RefuseLA" setting would be the one that I'd think most closely matches what you're doing with Procmail: it stops accepting SMTP connections until the load goes back down.
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