In most instances yes you can. The only limitation is that we can't host email addresses that use another ISPs domain name. For example we use @btconnect.com as the standard domain name for email addresses hosted with us. Because we own btconnect.com no other ISP could create email addresses ending @btconnect.com. If you can't move the email address to us you can ask your previous ISP to forward any emails to a new BT hosted email address.
As long as your email addresses use your own domain name (i.e. firstname.lastname@example.org) they can easily be moved to BT.
For more information, please see Domain name transfer after switching to BT from another ISP.