I've used Mailchannels at several different companies, with one installation that does over 60 million outbound emails per month. I've run my own mail relays and know the pain of trying to prevent a few bad apples from ruining your sending reputation for the good senders. After using Mailchannels I don't think I'll ever waste time running my own outbound relays anymore. The amount of work required is not worth it anymore and I'd rather be spending time on other things.
The best part of Mailchannels is that it segments reputation by the individual sender email/domain instead of by IP/server. So one bad sender won't affect mail delivery for another sender that is sending legitimate mail. I don't know all of the behind-the-scenes technical details, but my understanding is that they segment relays so you get a different pool of IPs based on your historical reputation; good senders will get the A+ relays and questionable senders with frequent complaints will be pooled with other bad actors until proven otherwise. They also have access to a lot of aggregated data about spammers and patterns that I'm sure helps them stop malicious behavior quicker than something you'd be running yourself. On top of that, they've put a lot of work into creating some solid reporting and web based tools to get more visibility into where mail is coming from and what might need closer inspection. If you want to chat more about it, feel free to drop me an email. I'll be the first to say that I was skeptical about outsourcing this part of our infrastructure, but now that I've been using it for over a year in several different capacities, I regret not switching earlier given the time wasted running relays, rotating IPs, pleading with blacklisting companies to remove us, etc.
