Can I use hosting without transferring domain to you? If domain transfer is mandatory: —what is needed to transfer domain to you? —How can I process mail, incoming to that domain?
Yes, it is totally possible. You should just add NS records (name servers) for that domain at your domain registrar after uploading all files to our hosting.
Settings for processing incoming mail are in hosting control panel. There you can access web interface for mail. Also you can connect to the mail server using any mail program via POP3/IMAP protocol.