MAPI supports a limited form of regular expression notation. Regular expression notation is a compact way of specifying a group of strings that all match some criteria. A target string is said to match the regular expression if it is a member of this group of strings. Regular expressions are character strings in which plain text indicates that that text must exist in the target string, and special characters are used to indicate what variability is allowed in the target strings. MAPI uses the rules for regular expression matching only when the relational operator being used to compare strings is RELOP_RE.
Regular expressions are constructed of one or more single character regular expressions. A single character regular expression tests one character from the target string against one or more characters specified by the single character regular expression.