[Mailman-Users] slow "out" queue

We just moved a very old mailman infrastructure mailman to Solaris and sendmail. It seems, when a message is posted, the "out" directory doesn't seem to clear out fast enough.

1K archive 1K bounces 1K commands 1K in 1K news 403K out 1K retry 1K shunt 1K virgin

The size just stays like that forever and slowly decrements. When I look in /var/log/syslog (mail log of sendmail), I see deliveries going through. I do a 'truss' of the OutgoingRunner python process and I see:

% truss -p 11997 recv(10, 0x00748454, 8192, 0) (sleeping...) ... %

What is it waiting for?