Earlier quoted context omitted.
Note that @mailinator.com email addresses are blocked at a significant number of sites due to its popularity. Throwaway email sites that alternate between several different domains work best.
Mailinator has a ton of different domains. You can check them all from mailinator.com though.
Instead, the site will randomly show one of the alternate domains on every page load. At one point, it would even give 'gmail.com' and other legitimate domains as the alternate if you tried to scrape them too quickly (or rather, they hypothetically-yet-definitely-didn't-do that).[1]
Today, the alternate domains are shown as an image[2], and even that isn't a complete list, since other people can simply redirect mail incoming to their domains to mailinator.com. Mailinator explicitly condones this.[3]
[1] http://mailinator.blogspot.ca/2011/05/how-to-get-gmailcom-ba...
[2] http://www.mailinator.com/get_alt_domain
[3] http://mailinator.blogspot.ca/2007/10/new-mailinator-alterna... (end of second paragraph)