Modify a Regular expression to include underscore character

Need the regular expression to support an additional pattern along with existing ones. ^(?(")(".+?(?<!\\)"@)|(([0-9a-z]((\.(?!\.))|[-!#\$%&'\*\+/=\?\^`{}|~\w])*)(?<=[0-9a-z])@))(?([)([(\d{1,3}.){3}\d{1,3}])|(([0-9a-z][-0-9a-z]*[0-9a-z]*.)+[a-z0-9][-a-z0-9]{0,22}[a-z0-9]))$ Refer this page for more info on this regex: [login to view URL] test_@[login to view URL] is considered invalid. This pattern needs to be added without breaking existing valid email recognizitions.