Rule conditions are described in terms of MAPI SRestrictions. Rules are tested and fired in a sequence defined by the PR_RULE_SEQUENCE property. The Microsoft Exchange Client rule provider uses gaps between rules as a mechanism to allow rules to be reordered without replacing all the sequence numbers.This means that the sequence numbers need not be consecutive.
An error will be returned by the IExchangeModifyTable interface when rules are saved if either of the following conditions exists: