220.127.116.11.1 Processing Out of Office Rules
If a rule (4) has the ST_KEEP_OOF_HISTflag set in the PidTagRuleState property (section 18.104.22.168.1.3), the server MUST keep a history of recipients for that rule (4) and check whether the sender of the delivered message appears in the list for that rule (4). If the sender is on the list, the server MUST NOT evaluate the rule (4). If not and the rule (4) condition evaluates to "TRUE", the server MUST add the sender to the list of recipients (2) for the rule (4) in addition to executing the rule (4) action (3). If the rule (4) condition evaluates to "FALSE", no additional action (3) needs to be taken.