Simple answers to FAQ
Some IPs are blacklisted. Does that mean there are bad proxies?
Residential or mobile proxies will not get blacklisted unless you use SMTP to spam. With these types of proxies, blacklists can be disregarded.
If you use a blacklisted datacenter proxy, you will not be able to use SMTP servers effectively.
In blacklisted proxies because providers distribute one external IP to hundreds of users.
For example, one user has a virus on the computer and sends letters, the IP address falls into the SMTP black list (and correctly, there should not be mail servers on user computers, where should they be in a normal situation? User computers should not send letters, this is the way it works mail part internet).
In the case of hosting, which can be a mail server, everything is obvious, if the IP address is not resident, but belongs to the hosting, blacklists will protect against spamming from servers.
If Google / FB and others are banned, it’s not for the SMTP black list, but for the data center / hosting ip, which also has a low trust scrore
(you can check the trust score, for example, at https://getipintel.net/ )
You can see the type of IP to which the proxy belongs on the site https://proxyleak.com -> Extended version -> IP -> Type
Most IP verification services do not show and do not bind between types of IP addresses, because access to databases with types is many times more expensive than profit from the verification service itself or related products sold on it (for example, VPN)