Depending on what "Blacklists" you're referring to, our IPs could be listed in places where it doesn't impact mail delivery. If you're referring to something like Backscatter, we've been listed there for years. You have to pay to be removed, and we aren't going to pay only to be listed again. If it's a legitimate blacklist, we'll contact them to request delisting as soon as possible.
The most common blocking is by AU ISPs who have strict rules. Users report emails as spam that they receive through their mailmap forwarding, which causes the ISP to block us, even though we're just the relay. Why don't we block spam? We do. We block a lot of spam but can't block spam that is using legitimate sources to send their payload. I'm referring to compromised mailboxes that've had their passwords hacked and are now sending spam through your mailmaps.
