Disallow RTF Textmessages

Good Day,

is it possible to disallow to send Messages in RTF Format so it's only possible to send Mails in Plain text Format?
What i know, how to lock Sending HTML Messages in the Groupwise Client Option.
But if the Message is send internal, it will be in RTF.
If the Message is send to an External E-Mailaddress it is in Plain-Text.

Is there any solution to use only Plaintext?

Best Regards Basti

GW Client 8.0.2
OS Revision Linux Release 2.6.16.60-0.42.5-smp
GroupWise Agent Build Version 8.0.2-96933