To use your webhosting email service you need first enter your email (website) domain(s).
Domain
Only enter your domain to receive emails with it. Optional you can enable a spam filter/protection.
Email Mailbox
Full mailbox service. Create your own Mailbox(es) for your domain(s). You can use your email account with webmail or your email program (IMAP, POP3, SMTP).
Email Catchall
A simple and fast solution is email catchall. This means, all emails from *@yourdomain will send to your email account (any external service). Usefull when you have much websites, settings or don’t know how to configure a full-service mailbox.