Hmm...

I've been pondering this on and off for a couple hours since you submitted the PR

I think the error message might just be a typo - let me explain my reasoning

Currently the tool doesn't allow

/test.html	http://example.com/test2.html

Your change would allow that but disallow

http://example.com/test.html /test2.html

I can definitely come up with a reason for the first not to work. - it doesn't make clear if the host changed.

The second one I can reasonably safely assume the host did not change - so we definitely don't want to block that.

I also wonder if a FROM specifying a host should always verify the host of the request - which we currently only do if both TO and FROM have hosts.

I'm half wondering if a new setting, some sort of host-check strictness option is in order here…

Let me ponder some more and get back to you.