Index: rules/20_ratware.cf
===================================================================
--- rules/20_ratware.cf	(revision 326038)
+++ rules/20_ratware.cf	(working copy)
@@ -89,7 +89,7 @@
 
 # Outlook IMO (Internet Mail Only)
 header __OIMO_MUA		X-Mailer =~ /Outlook IMO/
-header __OIMO_MSGID		MESSAGEID =~ /^<[A-P]{26}A[AB]\.[-_\w.]+\@\S+>$/m
+header __OIMO_MSGID		MESSAGEID =~ /^<[A-P]{26}A[ABC]\.[-\w\.]+\@\S+>$/m
 meta FORGED_MUA_OIMO		(__OIMO_MUA && !__OIMO_MSGID && !__OUTLOOK_DOLLARS_MSGID && !__UNUSABLE_MSGID)
 describe FORGED_MUA_OIMO	Forged mail pretending to be from MS Outlook IMO