Keyword Expressions

Keyword expressions can be:

  • Groups of literal text characters

  • Patterns, defined using symbols (regular expressions) that describe a range of possible groupings of text

  • A mixture of literal text and symbolic patterns

For example, a keyword expression might be a single word, a phrase, or even a substring; or it might be a pattern that defines a more general grouping of text, such as an asterisk used as a wildcard to stand in for any text of one or more characters in length.

Regular expressions, often called regexes, are sets of symbols and syntactic elements used to match patterns of text. The symbols stand in for character patterns or define how the expression is to be evaluated. Using regular expressions is sophisticated way to search for complex character patterns in large blocks of text. For example, suppose you want to search for the occurrence of an email address—any email address—in a block of text. You can build a regular expression that will match any pattern of text that has any valid name string, followed by an @ character, followed by any valid domain name string, followed by a period, followed by any valid domain suffix string.

Trend Micro Email Security uses a subset of POSIX regular expression syntax.


If your expression includes the characters \ | ( ) { } [ ] . ^ $ * + or ?, you must escape them by using a \ immediately before the character. Otherwise, they will be assumed to be regular expression operators rather than literal characters.

This help system contains a brief summary of common regex elements, but a thorough guide to regular expression syntax is beyond the scope of this help system. However, there are many sources of reference information available on the Web or in books.