Email sent using rules chops characters off email from address
I tracked the problem down to the mimemail module.

In mimemail.inc there is a function called mimemail_headers which contains this:

  if (preg_match('/[a-z\d\-\.\+_]+@(?:[a-z\d\-]+\.)+[a-z\d]{2,4}/i', $from, $matches)) {
    $headers['Return-Path'] = "&lt;$matches[0]&gt;";
  }


The {2,4} at the end of the regex caused it to chop the les off of meeples. Changing it to + fixed the problem.