[I.P.] did not issue MAIL/EXPN/VRFY/ETRN during connection to IPv4

I have only seen threads in regards to these notifications from spambots. However, there are several legitimate services that I am not receiving mail for on my mail server, and they error out with the following message:
" [I.P.] did not issue MAIL/EXPN/VRFY/ETRN during connection to IPv4"
I have no clue how to fix this problem. I have just rebuilt the file to make sure something did not get mangled the last time I upgraded. However, it is still bouncing real mail.

Chris KQ6UP
Can you identify any specific mail servers which trigger these errors? Also: what FreeBSD version do you use and do you use Sendmail from the base system or did you install a version through the Ports collection? And speaking of which: does your MTA actually use authentication or some kind of relay?
I was able to get it working by using a fresh mail configuration from a freshly installed system. It was probably the dns blacklist server configuration. The list was SUPER old. A whole bunch were probably timing out.