http://projects.puppetlabs.com/projects/1/wiki/Puppet_Augeas

Set a mail alias with augtool:

set /files/etc/mail/aliases/*[name = 'www']/value "webmaster"
save

To do this in puppet the manifest should look this.

 include augeas

 augeas { "wwwwalias":
  context => "/files/etc/mail/aliases",
  changes => "set /files/etc/mail/aliases/*[name = 'www']/value 'webmaster'",
}