Remember that your downline is made up of individual and independent business persons whose temperaments you may not know intimately. For that reason, whatever you may have intended to achieve by your so-called emails constructive criticisms may at times backfire with very negative results. In addition to that, many people do not like criticism anyway, no matter how positive and constructive. Try to avoid a situation where some members of your downline may actually be asking “who the hell does this guy/gal think he/she is?”
My best advice therefore is to avoid criticism all together. Restrict your interaction with your downline to purely advisory role. Simple!