Email, Slack, Microsoft Teams, etc. All great solutions, but then you have your vendor management efforts scattered in various places. Use the Chat Rooms to allow employees to communicate with each other and ensure your information is better centralized.
Every vendor & diligence review gets their own chat room, with access limited to those that can access the item.
The "Your chat rooms" page shows all chat rooms that you're a part of and when a message was last posted.
Invite others to join the chat & elect to be notified via email when a new chat message is posted.
For diligence reviews that have been assigned to a review committee, there can be a separate chat room only available to committee members. Post & respond to questions regarding the vendor's responses without firing off a dozen different emails.
All chat rooms can be saved to PDF for archival purposes.