Corrupt HTML output

Hi,

We replaced the standard CKEditor-driven WYSIWYG in Salersforce with the full version so we could use the Source editor. The content is passed to a mail server. However if we cut and paste either HTML text into the Source editor or content into the main editor, the output from the mail server has encoded certain characters to ASCII, which breaks functionality.

Note that the corrupted code is not visible in the Source or main editor, but only in the email source based on the content.

What I specifically see is that equals signs are getting replaced with the ASCII equivalent =3D. The same code manually typed into the Source editor does not produce this behavior. When I view the headers and source received by email, I see that the encoding has been set to:

Content-Type: text/html; charset=utf-8
Content-Transfer-Encoding: quoted-printable

In contrast to the settings I see when I manually type in the same code:

Content-Type: text/html; charset=utf-8
Content-Transfer-Encoding: 7bit

The changes experienced do make sense in the context of the quoted-printable encoding, so I suspect that the mail server is applying that encoding in a way that corrupts the HTML. 

Does this make sense as a plausible cause, and if so, is there a way to either change the configuration for the encoding or to safely cut and paste content and HTML into the editors?