Parses email message header fields for valid Internet email addresses, comments and aliases.

A comment is a string surrounded by parentheses, as defined in RFC822, 3.1.4.

An alias is defined as any substring which appears to the left of a legal email address: for example, the string "this is an alias" in "this is an alias <an.email@address.com>".

For email addresses, the string being parsed: 1) must contain an @ character, surrounded by valid address characters; 2) may not contain more than one address or @ character; 3) may contain aliases and comments.

Note the following about the implementation of this class:

1. Functions that test subject lines, ValidSubjectLine(), and alias names, ValidAliasName(), were initially written to test that the strings did not contain characters outside a limited ASCII range. Unicode characters are now allowed, so these functions now always return true.

2. Of the four overloads of GetValidInternetEmailAddressFromString(), only the first has a meaningful implementation.