Problem with SimpleNews and line limit error

Hi all,

I have been using Simplenews to send out newsletters for months now.  I send them with the body in full HTML, and usually it all goes fine.

I did nothing truly different, but this week every single email got rejected with the error that a line in the email was too long (too many characters).

In the WYSIWIG editor when I add the content, the lines are obviously not too long.

But when you open the HTML view the code and text presents in one line.  Is this the problem?  Or do I need to fix something else?

Drupal version: