Plain text recipients in LetterMark 5.x allow you to specify individual email addresses which will always use the plain text version of a template. This is generally used when a sending to someone who prefers not to view their messages with HTML, such as users of mobile devices which aren't capable of displaying HTML messages. It may also be useful when sending to someone with an over zealous spam/anti-virus filter or to automated systems which may get confused by LetterMark HTML templates.