Possibly because it will try very hard not to just throw mail away. Are the files qf* and df*, or Qf* and Df*? The latter are files that Sendmail won't process - it's essentially put them aside for human intervention.
There are 16000 odd Qf files and 21 Df files. Most of the rest are xf, df and qf files.
Sendmail tried to deliver that double-bounce, and failed because of an error from your local delivery agent. Does the Cyrus side log things anywhere? It ought to.
It appears that the problem pertains to "554 5.6.0 Message contains bare newlines" errors. Cyrus will not store mails like this and as the postmaster account is on a Cyrus server it bounces the bounce and sendmail panics. I have the E=\r\n def in my cyrus mailer definition too..
Aside from the obvious (and I'm sure a million people will tell you all about the evils of Sendmail; I'm not one of them), it seems there's a problem with the Sendmail/Cyrus integration here. Hunting that down might shed some light on the rest of it.
I'm not fan of sendmail but it is all I know. :) I've never bothered to learn postfix or exim et al. And getting them installed on this shitty RH7.1 server could be tricky. Regards -- Oliver Jones » Director » oliver(a)deeperdesign.com » +64 (21) 41 2238 Deeper Design Limited » +64 (7) 377 3328 » www.deeperdesign.com