Undefined offset for Return Path when sending mail

+1

I'm also getting the same problem since upgrading the Drupal 7.15 and installing an update of Simplenews. The error is occuring while sending emails using Rules, though for me it was reporting line 68. This is the offending section of code:

    // This may not work. The MTA may rewrite the Return-Path.
    if (!isset($headers['Return-Path']) || $headers['Return-Path'] == $default_from) {
      preg_match('/[a-z0-9\-\.\+_]+@{1}[a-z0-9\-\.]+/i', $from, $matches);
      $headers['Return-Path'] = "<$matches[0]>";
    }

Line 68 is the $headers['Return-Path'] = "<$matches[0]>"; I am using the Domain Access module, which may be relevant...

My recollection is that I had this problem before, but after I visited the configuration page of one of the modules in question, and re-saved the configuration, the problem was solved. Trying to figure out which.

Could be a duplicate of #1813348: Sendmail invoked with empty Return-Path. Testing.

I'm getting this error in trying to send an email to reset the password. Nasty as it prevents me from recovering user1's password.

Marking as duplicate of #2129149: Undefined offset in mimemail_headers.