We use katabooost to communicate with our customers about their orders in an easy way - especially when we are working through timezones! It is very customizable so that it fits your exact needs/requirements perfectly without any hassle at all!! I have not found anything yet which i dislike from this software package (yet).
So far everything has been great! The support team was always there whenever needed as well!! Perfectly suited solution if you need communication between multiple people within one organization or different ones across borders / countries.