If you are offline and someone messages you you should be able to send a message back automaticly (already written and saved as an automatic reply,and you should be able to turn it on and off)

e.g saying " I am away wont be able to send any orders untill 7th of march in the afternoon" or " I am available between 6 am -6.30 am ,7pm- 10pm"

So people know when they will be able to contact you