The IRS maybe checking your email without a search warrant and you may not even know it. A FOIA request filed by the ACLU (American Civil Liberties Union) revealed their policies which allow them to take such actions.
The IRS usually only will check if they believe that there are some discrepancies with your taxes but you will never know, unless they take you to court. Government agencies and law enforcement have the freedom to check your social networks because what you post on there is essentially available for the world to see.
Moral of this video: Be careful what you post online.