You may not know it but your Internet provider may use Spamhaus to filter the emails sent to you. Spamhaus can arbitrarily decide to block entire blocks of Ip addresses. Then you will never receive an email from users of those IP addresses. You will never know why someone didn't reply to your email: that person's email simply cannot be delivered to you.
Please ask your Internet provider NOT to use Spamhaus. Spamhaus is a popular spam-control software but it is a terrible tool because it blocks entire IP addresses: to punish one spammer, it blocks millions of people.
It's like throwing in jail an entire town because someone in that town has committed a crime.
Spamhaus will never penalize the IP address of a major corporation, no matter what they do, but it often blocks the IP address shared by independent websites like this one. Spamhaus just doesn't care about the damage it causes to small independent operations.
Spamhaus claims that it is run by people who are "investigators, forensics specialists and network engineers". As it is often the case with scientists and engineers who think they can play God, they can easily turn into Internet Nazis who have no respect for basic human rights. Note that, as they claim, they have "one of the largest DNS infrastructures in the world". And that's terrifying.
I don't know whether Spamhaus' staff has profited from spam email, but certainly they have never been punished for the damaged they caused to people who never spammed in their career. It's like a police officer who is never punished for all the innocents he shot.
Please ask your Internet provider NOT to use Spamhaus. The damage caused by Spamhaus to the cultural websites of the Internet like mine is not negligible.
They are one of the worst kind of censorship: you can't even argue with their stone-age algorithm. And they call "spammer" anyone who accuses them of being a dangerous organization. I may be branded a spammer on Spamhaus' website because of this page that you just read, just many other victims before me.
This is what may happen if i reply to your email and your provider is using Spamhaus:
You will never know that i replied.