[linkregister]

Thanks for responding. Great explanation! I agree that adhering to the SPF standard has diminishing returns as support is added for the more esoteric macros. Support for every single macro in the standard is almost certainly unnecessary.

I've seen a simple recursive descent parser to process SPF records, but never considered it could be done with a VM or a stack-based machine. Even with the DNS Lookup Limit, it appears you made the right choice to avoid the call stack for a fully async I/O interface.

Your coding style is simple but since I have never studied a VM before, I have trouble telling what's going on. You've inspired me to learn more!