I have some legacy IoT devices in the field that directly talk to sendgrid. Would be a big pain if I had to recredential them. So I stayed on sendgrid.

My newer devices get their email proxied through a proxy I host. It was a dumb mistake on my part to tie myself to so tightly to a SaaS vendor.

How much worse do you think it'd be if you had a static IP and were essentially having to manage your own sender rep yourself? Google and microsoft postmasters are unlikely to pay much attention to someone running an IP maybe sending a few thousand emails a day.