Notification emails and SMS are unreadable on cellphones

Outgoing text only email messages and SMS messages are encoded as MIME with Content-Type: text/html and with Content-Transfer-Encoding:Base64. All 3 are not supported by some email-SMS gateways and create impossible to read data on cellphones.

The message looks like:

Subject: Linux: Critical
Mime-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: base64
Lines: 1

ASDHJDHJVNSDFFWERWER...

The decoded base64 is not plaintext as it contains some "
" html-tags not expected here:

Ursache:
1. webserver1 ist nicht aktiv

Is it possible by editing internal configuration files to use Content-Type: text/plain with Content-Transfer-Encoding: quoted-printable?

Version: Applications Manager 7, 7300 (German)