bsd port assignment

[Donnie Love]

I've got a question concerning port assignment on a BSD 4.2 
(Sun 3/160) machine. I've got an application which I want to 
run on port 21. I also want ftp to run on another port. I've
changed /etc/services to point my application to port 21 and
ftp to point to port 517. When I ftp to my system, I get the
"new" application (what I want) and everything looks fine.
I can ftp to my system if I specify port 517 (OK too). 
However, if I try and ftp out of my system, I get a message
"ftp: connection refused". This is a local message because
I can telnet to port 21 of the remote system and it responds.

Does anyone know why this is happening and, more importantly,
how to fix it? Please respond directly to me as I am not on
the list.

-Donnie