We built a relay bit couple years ago. You can invite the bot into a private channel and then other users who are not part of the channel can use a form to send

We built a relay bit couple years ago. You can invite the bot into a private channel and then other users who are not part of the channel can use a form to send messages to that channel. The members of the Channel can then use the thread to answer. Works really well and has the effect that inter-department communication don't always need to go through the department heads. This could, of course be abused for spam, but so far it worked well.