Why won't it let me use my e-mail account?

Due to the nature of our product, we require a corporate e-mail address. We do not allow accounts to be established with e-mail addresses created using disposable or free e-mail services. These services include, but are not limited to, Gmail, Mailinator, MailCatch, and Einrot.

If you attempt to create an account with this type of e-mail address, you will receive this error message: