Just need to check it first (port 25) and use providers with good reputation.
Many years I got many VPS-based mailservers without any problems with IP block or similar problems. Just need to make initial setup of you server correctly.
Reputation services are not banning big ranges of IP addresses because of one stupid-spam server in providers network.
But if you can't deny free relay on your host, it's just your problem and no problem of your provider.
Just need to check it first (port 25) and use providers with good reputation. Many years I got many VPS-based mailservers without any problems with IP block or similar problems. Just need to make initial setup of you server correctly. Reputation services are not banning big ranges of IP addresses because of one stupid-spam server in providers network. But if you can't deny free relay on your host, it's just your problem and no problem of your provider.