My domain is a year older than Google itself and has been in continuous use for e-mail that whole time. The IP addresses it is on haven't changed in a decade. But that didn't matter. DKIM, SPF, DMARC, forward and reverse matching DNS, exactly four users who do not send spam under penalty of being buried under legal solicitations for green cards, and all the rest didn't help. Randomly getting sent to /dev/null for no good reason. And not enough traffic to qualify me to use their Postmaster utilities.
Three years ago I gave up and ported to Fastmail with a tear in my eye for the days when even the smallest net on the Internet could be a full participant.