Domain transfer

Hi

Currently we are hosting a website with one.com. I am interessted in purchasing Zoho One and create a new website with the Zoho Sites and incorporate all the features.

I had contact with one.com and they tell me that Zoho is not compatible with them. So i will need to transfer my domain to lets say GoDaddy. First of all is a transfer really needed, why is it that it would not be compatible?

Second, if i do need tot transfer, will i loose my mailboxes, mail adresses and mails?

Kind regards

Kevin