Plain-text digitally signed mail contains HTML part

When sending a digitally signed plain-text mail, the mime will include a html part and plain-text part. When the mail is send internally the GroupWise client will show the mail as plain-text and you can not switch to html. If the mail is opened via a IMAP client (e.g. Thunderbird) then this mail will be shown as html. If the mail is send externally, the mail also will be shown as html (even when this is also GroupWise).

This is solved in GroupWise 8 Support Pack 2 and later.