I assume, you successfully created a html-file from the excel-sheet. And I assume, you have a plugin (i.e. email-ext plugin) to add attachments to emails. Then I suggest, you add this html-file as artifact. Then you should be able to append this artifact to the email.

Details:

https://plugins.jenkins.io/email-ext/

Can Jenkins send mail notify with attachment?

https://medium.com/@gustavo.guss/jenkins-send-email-with-attachment-cec1e052583a