If it were me, I would not offer to send the data in HTML. That is a non-standard BAD IDEA.
A more standard approach would be to post the data to your partner in an XML file that you create based on a XML schema that both parties agree to.
Create the schema in XML Spy or your favorite XML schema editor, add reasonable content constraints and then review it with your partner. The XSD become the contract between you as to what you will be sending and can be validated on either side.
Post the XML document which adheres to the schema to your partner via pub.client:http.
Flat files (CSV’s) are certainly an option, but if the partner can process an HTML document, they can probably handle XML and you both will benefit from an verifiable, agreed upon structure.