I want to allow an external device through my firewall. This device does not have a static IP address but it does use a dynamic IP address name service.

Can I create a firewall filter rule to use the host name to lookup the IP address in order to allow this device through the firewall?

Thanks.

Simple answer, no!

I thought as much. Having looked at the manual I could not see an (easy) way to do this. The TELNET interface does give command line options to create/update rules and objects, I'll investigate that as a possible solution, although it does not look very straightforward.

Just create an IP object with current IP, and create firewall rule with this. Every now and then just edit the object with new IP.
I have the same issue with a client (RDP) and a set him up a dyndns in his PC. Every week I ping that dyndns hostname to view current IP. Not a good option, but a good and well paying customer!

Thanks. I see IP object is editable via the TELNET command line. I may be able to use this to automate a ping and IP object update using a scheduled Windows task. Maybe an Autoit script or even just a DOS batch file. Should be possible in theory at least!

You'd be better just getting a device that can do that i.e Palo Alto. You'll pay a lot for it though.