Mailinator addresses, and other "disposable" email service addresses, are often rejected by sites that ask for an email address to create an account.

There's sort of a race condition between how quickly new "anonymous" email services appear and how quickly they are banned by other sites.

Then just use temp-mail.org, they rotate domains very frequently, they have been around for some time now as well.

Similarly spamgourmet has been around since 2001 and other than some brief outages (around the time the founder was sadly struggling with a terminal illness and figuring out succession plans) it's doing fine.