Sitebuilder does not offer proper documentation on this matter. For anyone dealing with importing emails after moving their domain away from Sitebuilder the process is needlessly painful. This configuration can also be used even when your domain is on Sitebuilder, as their suggested server settings of service.yourdomain.com simply forward to the actual addresses listed below.
- IMAP: us2.imap.mailhostbox.com:143/993
- POP: us2.pop.mailhostbox.com:110/995
- SMTP: us2.smtp.mailhostbox.com:587/465
- DAV: us2.dav.mailhostbox.com
Hope this saves you some time!