Good advice but this is a little dubious "For other internal communication use Slack". Use slack because it is beautiful and free, not because of security
For example, we use Trello for feature planning and tracking marketing activities etc., but have Trello post to a specific channel in Slack also.
Additionally, we use Intercom + Helpscout for customer support, and have those posting to a support Slack channel as well. Then there are the various Amazon reporting and deployment services which also post log messages to Slack.
In a nutshell, I can jump on Slack to check the overall 'big picture' view of my SaaS, but not have things get lost in the noise.
Email gives me a reminder to keep me organized.
And the two teams I worked on that use slack killed productivity by chatting all day and sending animated gifs.
Plus, people expect email to be asynchronous. With slack, I get a mixture of immediate and asynchronous requests. So every message breaks my flow while I determine the priority level.
That sounds much more like a people problem than a technology problem, if that's how they chose to spend the majority of their time on the job.
The links in question relate to:
* Searching on GitHub for Slack API tokens
* The Slack database hack
* How the rise of ChatOps can open you up to many more issues if someone gains access to employee's Slack accounts and the risk of third-party applications which might open up things you do to more entities than you realise