I’ve read through the post and the comments again, and it’s also that he doesn’t seem to want to train his users. They’re familiar with Gmail so he wants them to be able to use it. His users probably use their mailbox as an archive, and he doesn’t want to train them into understanding this is a bad idea, and he doesn’t want the hassle of dealing with ever increasing mail storage. At my previous job, we had Exchange Online, so 50 GB of storage. I was still explaining to my users, they should store their handled mails in archives if they wanted to be sure they would always have them. (Obviously stored on parts of their hard drives set up to synch to the fileserver which had daily backups)
All of these things are normal parts of an admin’s responsibilities. The only reason he’s getting away with his setup is because he owns the business and there’s been nobody there for the past 20 years to explain this would lead to problems down the line. (Or if there have been, he’s conveniently ignoring that)
Now they’re here, he’s blaming Google for what is probably the least evil thing they’ve done this year.





Honestly if anything he should focus on creating a solution where he can have DKIM active. He has dmarc and SPF, but not DKIM.