Was more referring to keeping track of all of the new temporary domain emails that are seemingly constantly being created, updating the database of them wouldn't be an issue but I'd imagine if XF had a feature specifically for this there would be people complaining that domain X wasn't successfully blocked. Maybe if there was some sort of official API that XenForo had for something like this which users could contribute to that each board automatically updated from every X days it'd be a bit easier to maintain since you'll have the ability to contribute to the list (with some sort of verification, probably)