If you look at the aggregate of the comments here, I think you get the idea. Its possible, but you have to constantly work at keeping it going with reputation,

If you look at the aggregate of the comments here, I think you get the idea. Its possible, but you have to constantly work at keeping it going with reputation, whitelisting, etc. and you'll never get to 100% deliverability ingoing or outgoing. Probably more like 70%-80%. The big guys whitelist each other. There are (very expensive) services for the medium guys, such as [Return Path](https://returnpath.com/ https://returnpath.com/) , that help you keep good relationship with the various ISPs. With many ISP's they even have a very specific whitelisting deal where you literally pay to be whitelisted...I think thats mostly the second tier ones like AOL, Comcast, Yahoo. Gmail for example doesn't play ball with that - but they will whitelist you if you follow all the rules and have a good reputation, which someone like Return Path can help with. Is the situation shady? Yes. But it rose out of a need for dealing with a real problem (spam), which you have to admit has gotten under control over the last 10 years. Bottom lime, I would use a 3rd party service.