The organization you're attempting to email is blocking your mail due to the office/home IP address of your location where you're attempting to send email from.  Unfortunately this issue is out of our control and cannot be resolved by us.

It is likely that the receiving organization has their email hosting through Network Solutions who actively blocks emails and provides the error message you received. In order to resolve the issue you need to notify the receiving party and have them contact their email hosting provider and "white list" your domain name (your website address).