Sorry I don't want to get into an argument here. The client(s) play no role handling requests (from the server?). All the server wants to know, whether to accept connection or not, is whether the IP address matches one in the allowed list. (Just to be clear I'm talking about the IP Access list in Settings under a [my] domain under Domains in the Wing FTP Server Administrator. Presently you type-in actual IP addresses. If the client is from one of the IP addresses the server accepts the connection request.).
What I want is for the server to accept connections from a client whose ISP assigns an IP addresses dynamically, i.e from time to time its IP address is different depending which line the client happens to get when its modem connects to the ISP, What the Dyndns (look this up on Google or whatever if you are not familiar with this service) service provides is the ability to use a fixed specific domain name such as joeblog.dyndns-office.com which is mapped to whatever IP address happens to be assigned to the client (Dyndns provides an updater software which runs on the client to regularly update the mapping of the dyndns domain name to the client's current IP address). So therefore if I can meaningfully type in such a dyndns domain name into the IP Access list then the client will always be able to connect to the server without my having to manually update its current IP address. Presently I have typed in a Dyndns domain name but Wing FTP does not recognise it (and it does not reject it as an invalid entry either).
That should not be too hard to do. Yes it is a reverse DNS lookup but that doesn't involve the client much if at all.
I'm surprised I've had to spell this all out.