If you don't want to receive any more messages from a certain visitor, you can ban them. To do this, click on the ellipsis icon in the upper right corner and select
A banned visitor won't notice anything and will think you still receive his/her messages, but don't read or answer them. As for you, you won't receive notifications on new messages from this visitor.
To unban a visitor, click on the ellipsis icon in the upper right corner and select