User sends email to a domain registered in plesk, gets over Maximum message size in plesk which results in mail not being delivered. However, notification about this does not arrive to users's gmail box. User expects the following notification : message size 1436008 exceeds size limit 1024000 of server mail.***.net[123.456.78.***]
It seems that gmail does not send such error notifications to sender. If the message was sent from a domain registered in another Plesk instance, the notification would be sent as was proven by tests.