Even if you can keep all that shit running fine for your organization, you can't make any guarantees with regards to these issues for all the other organization

Even if you can keep all that shit running fine for your organization, you can't make any guarantees with regards to these issues for all the other organizations on the planet. In fact, I would argue that you MUST assume that at least some non-trivial percentage of those other organizations are actually fucked up with regards to one or more of these areas. So, therefore, you must be even more conservative than you might otherwise have been. Even if everyone on the planet is a CMM-5 level organization, you're still going to lose the odd space shuttle or two. And maybe also some rockets. The forwarding problem has been with us since Internet e-mail was first created, and I don't see that problem going away. Ever. All you can do is decide how you're going to handle that for your own accounts where you set up forwarding, which may very well break e-mail coming from domains that don't fully understand the problem.