Problem occurs when sending html newsletter issues.

When creating a lot of content in the editor, attribute_view_gui generates all of the html code on one line without any linebreak characters (CR/LF).

It turns out that Sendmail has a limit for allowed line lenghts. When trying to send a longer line Sendmail inserts an exclamation mark in the content and also adds a linebreak.

This corrupts the content in a very unpredictable way.

Steps to reproduce

Create a newsletter issue with quite a lot of content and send it out through Sendmail as a test mail to your email address.

Look through the received email after exclamation marks and unpredicted line feeds.