Gmail/hotmail/live/Yahoo/GMX are used normally by users on this site, so you can't really ban 'em. Throwaway addresses are dumb domain names like shoppingsite dot xyz, you'll realize it.
Thats just it most of the spam we get comes from legitimate email clients as @Angel said and there is no other pattern than that. We ban, blacklist and IP Ban every throwaway domain name we come across and those are thinned out over time before another load pop up. However every now and again we get an influx of bots all from those legitimate sources that just have to be manually removed and banned which they are as soon as we spot them or they are reported and there has been thousands over the years. Somewhere in the region of 3,530 banned spam accounts here (177 pages worth) and im not sure thats even all of it. Spam like this has been reoccurring on every forum we have had over the last 18 years in the same manner and difficult to find a complete solution.