Microsoft puts Slack on internal list of ‘prohibited and discouraged’ software
geekwire.com
geekwire.com
Kind of like if a company ran 1000 MySQL instances and then a new engineer wanted to build a new service using Postgres because they were most familiar with it. Adding more different tools to the stack is technical debt.
If the people in your company are using a competitors product, aren't you better off letting them do that to be most productive while at the same time learning why they are using those products in order to make your product better?
Banning slack makes sense, they shouldn't get to use it if they're going to force their mess on everyone else and pretend like it's just as good and easy to use.
I can confirm that this is not true at all and one of the big team in Microsoft completely use slack even today and will be using going forward without any change.