do you do this personally? i've tried and found the barrier for entry is through the roof. if you don't configure everything just right you end up on gmail's spam blacklists and nobody gets your emails. and good luck getting off the blacklist once you're there.
i would love advice from anybody for self-hosting a reliable email server that the major carriers won't treat as a second-class citizen.
The barrier to entry is certainly higher than setting up a web server, but it's not too hard.
Advice for improving deliverability would be to add SPF and DMARC records for your domain (don't worry about DKIM).
Other than that, if I end up in someone's spam filter, I tell them to fix their spam filter. If your spam filter is classifying legitimate emails as spam, it's a bad spam filter. Doesn't happen often though.
They can still collect all the info you provide them directly, but it's a bit different than cross-referencing your gmail account with your phone's location history and your google search history, paired with your Google calendar travel plans and emails about shopping list updates for your Amazon account.