Absolutely agree. Even when in the same reporting chain, I'd consider it quite bad form because it leaves the people in between with reduced visibility, and often they might have information that makes them prioritize differently or assign different people.

You can get away with some reduced formality when addressing people reporting in to a layer below you but on another team, but "get away with" being the operative part. You will not get away with bypassing managers - even if you manage to sneak it past them now, it'll make people look out for future attempts.

Sometimes if you know everyone well it may be ok to e-mail someone direct and cc their manager and address it to both and suggest the person you're sending it to would be a good person to carry out the work, but I'd take care to make it clear it's up to said manager unless I have very strong reasons to ask for a specific person and then too the manager should at least be informed..

I've been on both ends of this, and more than once told off my managers for bypassing me because of the disruption caused.