There are tons of lists that are regularly updated that list all published mailinator.com domains. While it's true you can set up a new one on a subdomain of your own, as soon as you publish it to mailinator and it enters the rotation of the domains that come up, it's easily added to the lists and blocked. There's even a commercial live list with plugins for most email systems that blocks on any of the hundreds of mailinator-listed domains as well as over a thousand other disposable email domains.

Heck you can just write a script to refresh the mailinator.com homepage to start pulling out domains to block: @veryrealemail.com, @chammy.info, @mailinator2.com, @spamthisplease.com, @sogetthis.com, @mailinator.net, @binkmail.com, @sendspamhere.com, @spamherelots.com, etc.

No, it's actually super easy to block it if you're clever enough ;)