There's something both positive and negative to share about deliverability with any service.

For most users, our email services thrive off the communal/shared IP environment. For its success, it really depends on the behavior and marketing decisions that of our customers in order for deliverability to be high.

So, let's pretend email is like a river and each message are the fish trying to go upstream. The most current there is behind them (volume), the more successful the fish will make it to their destination. But if there's a flood of new current (say, a massive untargeted blast), they fish might be pounded into the bottom without making it to their intended destination. Consistency, quality and customer expectations are key to being successful in email marketing -- not necessarily the pool of IPs.

Respectfully, any email service provider will tell you 99% deliverabiliy. It's just a sales gimmick to attract those with poor deliverability. Just like Viagra attracts men who want to give their partners more lovin' -- it won't happen, and if so, for only a short period. The bottom line is behavior, also known as sender practices if you want to visibly achieve higher deliverability with ANY email service provider.

~Joe