Moved this here as this is an ioFTPD question and not a ioNiNJA question...
I'm not sure what problem you are trying to solve but I assume it's using a dynamic dns address so I'll address that. It looks like you already have Dynamic_DNS_Lookup = ALWAYS which is the first thing you need.
To enable normal SiteOps to use dynamic hostname lookups you need to allow that with a Secure_Ip rule. Check out rule #4 in the default .ini file.
Code:
# Allow dynamic :ident@foo.bar.com style masks
Secure_Ip_4 = 1 2 0 G1M
NOTE: You must have rules 1-3 active before it, if you don't just go ahead and rename this to the next free number so it might end up being Secure_Ip_2 or whatever. M flagged users can always set any hostmask (you will see an override message when you do this).
KEY POINT: Pay special attention to the very first character (the ":"). That's what tells the server it must lookup the IP address of the hostname for that user every time they login since it might be different each time...
The user's hostmask in your example should be ":TEST123@name.dyndns.org". Check out 'site help addip' which I believe has more info and examples. Also be aware that the Reject_Unknown_Ips option doesn't play well with dynamic hostmasks so that's why I invented the knock feature if you really have to lock down the server.