Allowed login type
This setting determines how the administrator for this domain is allowed to log in, by modifying their 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.