This setting determines how the administrator for this domain is allowed to login, by changing his Unix shell. The default available options are :

Email only
  Both FTP and SSH logins are blocked, but POP3 and IMAP will work.
Email and FTP
  The user can connect via FTP, but not via SSH or telnet.
Email, FTP and SSH
  Logins via FTP, SSH and telnet are allowed.

However, these can be customized by the master administrator on the Custom Shells page.

Because this feature works by changing the virtual server Unix user's shell, it assumes that your FTP server uses the `/etc/shells` file for authentication.