rlinetd: how secure?

[Sebastiaan <S.Breedveld@ITS.TUDelft.NL>]

Hello,

I am using rlinetd as replacement for inetd on a firewall. With
rlinetd you can deceide which inetd services are allowed to be available
for the inside and which for the outside world. 
When I do a nmap localhost, echo, discard, daytime, chargen, ftp, telnet,
smtp and time are available (and ssh as daemon). 
When I do a nmap from the internet, only ssh is available.

Now my question: how secure is this daemon, i.e. is it virtually
impossible to penetrate this daemon from the outside world?
Is it a good idea to run rlinetd on a firewall? I want to keep telnet,
smtp and ftp available for my lan.

Thanks in advance,
Sebastiaan