I use mailinator.com for most signups unless I'm sure I want to keep using the service. If I like it, I will change my email later (if possible). Unfortunately

I use mailinator.com for most signups unless I'm sure I want to keep using the service. If I like it, I will change my email later (if possible). Unfortunately this site tried to be clever, so I had to use one of the alternative domains. I don't understand the thought process behind blocking mailinator. It must surely be better to have a potential customer, than blocking them because they don't use a "real" mailaddress?