Ask HN: Solution to the problem with collaboration tools

Many of you must be using collaboration tools at work - Slack, Asana, Smartsheet, Comtify etc. The problem with all these tools is that all of them exist side-by-side emails. This is because none of these tools takes care of external communication and email is the only medium useful to communicate with people out of one's organization.

So how if we build a collaboration tool which also serves as an email client / email service provider? Won't it be an ultimate killer app for all collaboration tools / email service providers / email clients?