How to confirm hosting?

Thank you both for your help and advice. I’ve passed the SPF concerns off to my MSP, and we’re looking into them. I recognize some of the domains listed but have no idea who all those IP addresses belong to!

We finally found the missing site. During all of the turnover that occurred right after Covid, we had some miscommunications that resulted in the site being abandoned with a company that used to manage our main site. That company recently “cleaned up” old abandoned sites.