Why are my logs filling up with "Milter change: header..." entries?

Symptom: I am running MIMEDefang, but now I am getting a lot of messages in my syslog that look like this:

Milter change: header MIME-Version: from 1.0 to 1.0

Cause: It is actually the Milter engine of sendmail that is logging all those. To reduce the amount of logging, try putting this line:

define(`confMILTER_LOG_LEVEL', `8')dnl

in your sendmail.mc file and then re-generate your sendmail.cf.