The code exists to read the user's word wrap width preference: if (NS_SUCCEEDED(rv) && prefs) prefs->GetIntPref("mailnews.wraplength", &width); // Let sanity reign! if (width < 10) width = 10; else if (width > 30000) width = 30000; But the calculated width is never passed anywhere. In addition 30000 is a very abitrary number, not supported by any of the RFC's relating to creating plain text (text/plain) messages. I have attached a patch that moves this code to a place where it can have some effect, rationalizes the limits to match the RFC's, and allows specification of 0. All this works perfectly with our without format=flowed text. The existing issues with utf-8 are not affected. Plese consider applying this patch.
*** This bug has been marked as a duplicate of 155219 ***