Delimiter is a line of text added automatically in all the outgoing emails. It's required for the system to identify what should be cut, when a customer replies back to the ticketing system so that initial email message from the system is not added into customers reply.
With delimiter enabled the customer will understand that the message is generated by the system automatically, which doesn't give personalized approach in supporting your customers.
In UseResponse we have an option to remove the delimiter and the system will understand correctly what should be added as a reply. Please go to Administration » Support Channels and click on settings icon next to Email.
If you use other than English version of your community, delimiter is automatically translated using our built-in translation tool.
Note: if you use on-premise package, please make sure your server has access to tools.useresponse.com. Without the access, delimiter should be enabled in order to keep the replies clean in the system.