@jherazob @AlexanderMars @ehproque @rk @SecurityWriter @protonprivacy @nextcloud If they decide based on IP block reputation, you move to a different IP.
If they decide based on your domain identity, it's probably that you were actually spamming. I'd welcome any evidence to the contrary, but AFAICT a good 75% of the "don't host your own email because you'll get falsely accused of spamming and blocked everywhere" is from people who run businesses that want to spam (i.e. send anything other than receipts & account recovery emails).