They actually do end up banning each other's endpoints (specific IP addresses, not entire ranges) from time to time. --Even the big companies aren't able to pr

They actually do end up banning each other's endpoints (specific IP addresses, not entire ranges) from time to time. --Even the big companies aren't able to prevent their services from being used for spam even though they shut it down as quickly as they can. And usually the blocks are due to the blacklists like SpamHaus, rather than the email providers explicitly blocking competitors' endpoints.