Although E-mail systems are one of the most useful communication tools for business, education, etc., missing important E-mail messages becomes very serious problems. It is very useful filtering supports for users to pick up important messages or to neglect unnecessary messages. This work presents a method of determining the time priority for E-mail messages. Multiattribute rules are defined to detect complex time expressions and a set pattern-matching machine is proposed. It enables us to protect missing messages with important time information because the presented method can classify and rank them according to time priority measurement automatically. From the simulation results of determining time priority, it turned out that the presented pattern-matching method is from about 4 times faster than the traditional string pattern-matching method. From the results of filtering 5,172 sentences, it is verified that precision and recall of the presented method becomes 95% and 96%, respectively. From the experimental results of determining 10 highest messages among 100 E-mail, it is verified that filtering time by the proposed measurement is from 9.7 to 16.6 faster than that of a nonfiltering method.