It has to be unread and 6 months old, so if you just select all of your email and mark it as unread that is older than say 4 months, and go back every month and do the same, then yes technically you should be immune.
There are also sneak and peek warrants, and IIRC they do not have to notify you if they do that for the purposes of "national security". Plus, the only safeguard here is that they "promise" to obey by the rules, any one corrupt officer can just look at your email without warrant and nobody would really know.
I think the best protection is just to take your email off the server, and take your data out of the cloud. Anything on the internet is basically fair game under some law or another, or 5, or 20. If you have to use the cloud still, especially for email, just remove all email every 5 or so months and archive it.