Why do I already need an email address to sign up to Zoho mail?

Why do I already need an email address to sign up to Zoho mail?

Zoho is the only email provider I know of that requires new customers to already have an email address. This doesn't make any sense at all. I wonder how many potential customers have been put off by this. Please will you consider dropping this requirement? At least give new customers the option to nominate another account after they have signed up.

Cheers.