I have a similar impression from dealing with deliverability issues. Relevant providers usually just require a few days of sending legit mail and occasionally

I have a similar impression from dealing with deliverability issues. Relevant providers usually just require a few days of sending legit mail and occasionally asking to be unblocked, but there seems to be no chance getting into the inbox on GMail and Outlook with a "too low" sending volume. If it wasn't for regulations, I would have already given up and switched to GMail.