Contact Form 7 Same Domain: Additional Credible Sources Sought

I understand and respect the author’s decision to encourage users to use an email address that belongs to the same domain as the site in the From field. It helps you avoid looking like spam. I’ve followed this best practice since I updated the plugin last summer.

My difficulty is in convincing others that this is a good idea. For instance, I’m a webmaster for a website that has it’s email hosted by another IT company, and their tech insists that the sender should be anything but from the same domain.

I can definitely point them to the author’s page on best practices here: https://contactform7.com/best-practice-to-set-up-mail/
But I’m certain they will want additional credible sources, and I haven’t been able to find much with Google searches other than links to this plugin’s support. Can anyone help me find additional compelling evidence? Thanks.