It's obvious when your domain (well, the IP really) is blacklisted. You either get a nasty error from the mail system saying it didn't go through or that the se

It's obvious when your domain (well, the IP really) is blacklisted. You either get a nasty error from the mail system saying it didn't go through or that the server was unreachable or what have you. You're always going to get some notice that it failed. In that case I contact the recipient a different way and say, "hey, you're mail server is broken, can you please fix it?" Usually this means them contacting their mail provider and asking why they are blocking mail from someone they need to communicate with. If it's someone like Google, they'll realize they can't actually get any support and think twice about using Google for mail. A lot of people will say, "no they'll blame you for it not going through", but that's rare. Most people will be receptive to your insistence that you're trying to send them mail but their provider is in the wrong. Now, if you mean blacklisting in the sense that the server has shadowbanned you and is sending back "221 OK", then, again, you have an affirmative defense: "hey, you're mail server said it accepted the mail, can you please check with your provider on what they did with it?" In either case, this is actually not a good thing for the recipient's mail provider especially if they pay for that provider. "Why did you accept the email from the sender but not put it in my mailbox? Who else have you done that for? Why am I using you as my mail provider again?" I have a circle of influence... about 100 people. All 100 of those people would switch mail providers if I asked them to. And I think a lot of people have a circle of influence around this size as well. So there actually is an amount of control over these bigger mail providers. They will be receptive to "I just told your customer to switch because you won't let me email them" especially if it's widespread. In exchange for that "power", I make sure my mail server is as clean as possible and quickly respond to any notices sent to my abuse@ address.