I understand your use-case...its just that it's not a common one and the original design of the dynamic DNS service binds a domain to a device's hostkey...In other words, it would be a lot of work for very few people's benefit to break that 1:1 relationship and bind to something like hostkey:ethX.
Thanks for your post...I know it's the nature of forums to be asking for help, which necessitates there being a problem, but not enough people use these forums to post their positive experiences. Nice to see/hear...
The messages are located in the system MySQL database. If you're familiar with MySQL, use the access instructions.
I wrote the archiver, so you can blame me directly for the POS. We don't use it internally, so I've been reliant on feedback (mostly coming from partners and paid support or consulting) to know how it is doing in the real world.
I'm going to be rewriting parts of it when the conversion to a 6.x app is underway. I already have some thoughts on how to make it less dependent, or possibly completely independent of MySQL, which adds complexity and usually requires someone to keep an eye on things.