https://rt.cpan.org/Public/Bug/Display.html?id=51058

SMFIC_DATA is not implemented; postfix will fail on this.

the following patch partially fixes the bug:

--- Sendmail-PMilter-0.97/lib/Sendmail/PMilter/Context.pm	2010-02-08 12:01:52.225076154 +0000
+++ Sendmail-PMilter-0.97/lib/Sendmail/PMilter/Context.pm	2010-02-08 12:05:49.308047435 +0000
@@ -264,6 +264,8 @@
 				die "SMFIC_MAIL: bad packet\n" unless (@$envfrom >= 1);
 
 				$this->call_hooks('envfrom', @$envfrom);
+			} elsif ($cmd eq SMFIC_DATA) {
+				$this->call_hooks('data');
 			} elsif ($cmd eq SMFIC_EOH) {
 				$this->call_hooks('eoh');
 			} elsif ($cmd eq SMFIC_OPTNEG) {