Ok, but that system requires our domain to be trusted by Google. Since we're currently rate limited, I don't think we're in a position to ask for this trust.... To me it seems like it's better to generate mails which have validating DKIM signatures by stopping to rewrite subject and body.

However, it seems like something we'll need to announce. Bringing it up here so people get a chance to react to that. Also, if others have experience to the contrary, it'd of course be great to hear that this isn't a solution, if it isn't.... (Mark's remark that we can't modify the body either seems like a remark to that extent.)