When internet was born we catapulted into a new era with an unknown velocity. Around 25 years later we still appear perplexed and unclear about where we actually are.
I have this email signature.
"I recognize that my working day may not be your working day. Please do not feel obliged to respond outside of your working hours."
I try to encourage others to step away, and I have notifications on my own phone switched off after 6.00pm. It doesn't always work but for the most part, downtime is downtime. :)