It doesn't sound that bad. First, apparently only affecting 2-5% of mail. Secondly, everything works the same except for the absence of useragent and cache cont

It doesn't sound that bad. First, apparently only affecting 2-5% of mail. Secondly, everything works the same except for the absence of useragent and cache control headers (which aren't that helpful anyhow for analytics, especially when you're still getting those on 90%+ of your messages).