With 4th Office, you get email and Chat in one single place. So you don’t have to keep switching from inbox to other messaging apps and back.
To kick things off, ask the person you want to chat with to download 4th Office. Just click/tap their name, go to your chat stream and choose 'Send invite'.
You can also chat with people who don’t have the 4th Office app. They will receive Chat messages in the form of emails. However, they won't be able to send Chat messages to you or to any Team chats.