Emails: How to add sender to whitelist

this only works for one client, but it doesn't fix the problem for the entire domain

Which email client are you using?

I use webmail, usually read mail using chrome browser.

Regards

You could contact your email service provider and request them to add JotForm's IP addresses to their white list.

Here is a guide:https://www.jotform.com/help/145-Whitelisting-JotForm-IP-Addresses-and-Domains

You could also check this article:http://www.jotform.com/help/208-How-to-setup-email-alerts-to-prevent-email-bouncing-related-issues

Hope this information helps.