Added isAutoReply() method to InboundEmail

[io238]

Description

This new method ->isAutoReply() checks several email headers and/or the email subject line if it matches commonly used patterns that indicate that this email is an automatic reply to another email (also known as "Out-of-office-reply").

Checking the subject line is less accurate and can optionally be disabled by calling ->isAutoReply(false).

Background

Not all email clients/servers use the same header/subject formats when replying automatically. This method checks the most common ones. Also see: https://stackoverflow.com/questions/1027395/detecting-outlook-autoreply-out-of-office-emails

Example usage

Mailbox::from('[email protected]', function (InboundEmail $email) {

  // Only reply to email, if it's not an auto-reply
  if(! $email->isAutoReply()){
    $email->reply(new FeedbackReceived);
  }

});