While I was testing DCC Checksum , I discovered that some email messages are truncated and dcc reports that body part is missing with an error message "missing message body". I figured out that not only the body part is missing also the headers also truncated.
A quick investigation with tcpdump showed that spamc is sending truncated messages to spamd server which is passed to dcc server. A second tcpdump run on smtp server showed that some messages is rejected by qmail server with "451 See http://pobox.com/~djb/docs/smtplf.html." message. This was hitting a small amount of mails but the ones especially coming from hotmail.com.
I have quickly fixed the problem with djb's fixcrio application which comes with DJB's ucspi-tcp package. No more "missing message body" error messages anymore with dcc :)
Running fixcrio is easy. Just put the command before qmail-smtpd where you run it.