I spend a lot of time at my job developing emails for clients. We sends tons of emails for a variety of clients. To my knowledge, all of these addresses were acquired by ethical legit means. Most, if not all, are people who signed up to receive these emails. Some are transactional, some are informational, and some are purely promotional. They all are being sent from legit domains with strong reputations. But something has changed recently. Spam filters have cranked it up a notch. We have emails being blocked, filtered, and some blacklisted.
In come cases it's an issue with a specific email client. For one client, Google is directing the emails to their Spam folder. This is tricky because it's not a deliverability issue per sec, as they are getting delivered, but not really.
In other cases, sending domains are being blacklisted.
BTW, this is a handy tool to check domains, http://mxtoolbox.com/SuperTool.aspx
There are also others that are failing to pass specific server spam filters (Spam Assassin, mimecast, Postini, etc.).
This is an ongoing issue that comes with the territory, but in the last two weeks we've seen a big change. Emails that normally don't have these issues are being filtered, blocked, etc. These emails all have really good content. They don't have much spammy words in the the subject lines or body. They pretty much follow best practices across the board. They avoid the spammy words, have a good text to image ratio, have text versions, etc.
The sending domains have been properly warmed and large blasts are being throttled down to reasonable numbers.