"When mice march with elephants it's in the mices best interest to be cautious"
I've done a lot of a lot of email administration over the years, servers with 100,000s of accounts, and you walk a very fine line in being able to communicate with the rest of the world. Your IPs must exist in certain blocks (or at least not be in banned blocks). You must block outgoing spam messages at a much higher rate and quality than google/hotmail do. Get yourself blacklisted for any reason and expect to disappear from the internet, meanwhile no one is going to block the largest services.
I've done a lot of a lot of email administration over the years, servers with 100,000s of accounts, and you walk a very fine line in being able to communicate with the rest of the world. Your IPs must exist in certain blocks (or at least not be in banned blocks). You must block outgoing spam messages at a much higher rate and quality than google/hotmail do. Get yourself blacklisted for any reason and expect to disappear from the internet, meanwhile no one is going to block the largest services.