spamd stops after about 90 seconds?

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What do you know?  I got permission from my web and email hosting 
company (BlueHost) to run my own spamd process.  Cool! Now I can have a 
lot more control over the processing of my incoming mail, and I have 
access to the logs!  Well, after starting spamd, I was surprised after a 
couple of minutes when it mysteriously wasn't running any more.  After 
running some experiments, it seems it is indeed stopping after just over 
a minute.  Here's the command line I'm using to start spamd:

spamd  -d -i 127.0.0.1 -p 6615  -C /home/xxxx/.spamassassin 
--siteconfigpath=/home/xxxx/.spamassassin 
--virtual-config-dir=/home/xxxx/.spamassassin/%l -s 
/home/xxxx/.spamassassin/spamd.log --user-config -D -u xxxx 
--pidfile=/home/xxxx/.spamassassin/spamd.pid --timeout-tcp=0 
--timeout-child=0

I tried it without the last two timeout parameters and they don't seem 
to have any effect on this, and looking over the documentation, I 
wouldn't have expected them to.

Is this a normal behavior of spamd, that if it doesn't see any action 
from spamc for a while, it just quits?  By the way, I don't see anything 
in the log that tells me spamd is shutting down or anything like that.

I have been able to feed spamd some spam and it worked--I saw the scores 
and everything, but again, a short time after I did the test, alas, 
spamd shut down again.

What did I miss?