The blocking is a "service" provided by subscription software for that purpose, but it doesn't really work.
It's unusual for them to block all DMA domains, for a good reason. After trying a DMA like spamgourmet, then something like
10minutemail.com, it's almost as easy to go to yahoo and select a one-time address.
There are too many people who use yahoo and gmail for their primary personal addresses for them to be blocked. If that changes, most ISP access accounts permit enough addresses to make up a throw-away one.
(I usually add in a string of numbers or characters to the yahoo throw-away so as not to block out a meaningful address that someone may wish to use.)