"Changing address to a web based email account is not allowed"

I am getting the following error while trying to change my email to my Gmail address. Not having found any other way to contact the admins, I used the feedback option to ask why I am not allowed to do it. That's been a few days now without any response. Anybody else having similar issue?

" Changing address to a web based email account is not allowed, please use an ISP account "

As a matter of fact, I have not come across any other website which places restrictions on email domains. Why here? Cash?
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Abhi