I know that it's allowed; but — given that we're a B2B company serving highly-technically-literate customers — I don't think I want the business of anyone who t

I know that it's allowed; but — given that we're a B2B company serving highly-technically-literate customers — I don't think I want the business of anyone who thinks it'd be a good idea to use it even when it is allowed, given how it'd affect their own deliverability to imperfectly-implemented MTAs. (It's a similar "you're really relying on perfect competence from the whole rest of the ecosystem to get you out of this" feeling as e.g. putting a space in your user name — and thus your home directory path — in Linux. Sure, the core GNU/BSD/etc tooling has been tested for that use-case — but are you really going to trust random tools and shell-scripts to handle argument tokenization perfectly? Or are you just going to ditch the space to be safe?)