So don't attempt to register an email with comments in it, or for that matter with an ip host.
We need a much more restrictive standard for emails, but until we have that we have to accept that each site will have a competing not-completely-overlapping set of standards. So make sure your email doesn't attempt to do anything too funny.
I feel about this much the same way I feel about the endless proliferation of Markdown variants; if we could all agree on one simplification, sure, but the current situation where we haven't really stinks. For instance, ask early Gmail users about putting + in the email.
So while I agree with you in principle, in practice it seems infeasible. The differences bite in practice, unfortunately.
We need a much more restrictive standard for emails, but until we have that we have to accept that each site will have a competing not-completely-overlapping set of standards. So make sure your email doesn't attempt to do anything too funny.