Threat: Ex-girlfriend/boyfriend breaking into your email account and publicly releasing your correspondence with the My Little Pony fan club
Solution: Strong Passwords
Threat: Organized criminals breaking into your email account and sending spam using your identity
Solution: Strong passwords + common sense (don’t click on unsolicited herbal Viagra ads that result in keyloggers and sorrow)
Threat: The Mossad doing Mossad things with your email account
Solution: ◆ Magical amulets?
◆ Fake your own death, move into a submarine?
◆ YOU’RE STILL GONNA BE MOSSAD’ED UPON
All credit to James Mickens for the above.
My point being that if someone is that committed to compromising your air gapped system they're going to find a way. Especially if they can just slip the janitor $10,000 to put a USB labelled "Barely Legal Gone Wild" into the machine while vaccumming.