This variable controls whether or not Mutt will display the "personal" name from your aliases in the index menu if it finds an alias that matches the message's sender. For example, if you have the following alias:
alias juser email@example.com (Joe User)
and then you receive mail which contains the following header:
It would be displayed in the index menu as ``Joe User'' instead of ``firstname.lastname@example.org.'' This is useful when the person's e-mail address is not human friendly (like CompuServe addresses).