When you send message in Slack, you have no idea when it is read.
Sometimes you want to send really important message and it's frustrating when you don't get a reply for a long time.
With Envelope App your message will be hidden from recipient until special button is pressed, effectively confirming that message seen and read.
Just put special /envelope command in the beginning of your message.
We would welcome any feedback.
If you want to send a feature request, bug report or just want to say hi, please, drop us a line at firstname.lastname@example.org