You wont, it is personal choice for companies to chose what they will and wont allow in to their systems, you may have more luck giving one of the recipients a call to see why they have stopped it - they may point you in the direction of a specific link, page or item on the URL as a lot of the email scanners now, follow links and check content on the main link and if it spiders off with links to other sites or has adverts on the pages - these might trigger the block - but the recipient can be more specific as to the exactly URL their filter does not like.