That statement is used by lots of companies because they think it protects them from their emails being used as evidence. All it actually tells anyone is that they know nothing about law. The statement actually means nothing and can be ignored.
It is as if someone left a death threat on your answering machine and ended the message with a copyright notice. As if the court would throw it out or the criminal can sue you for sharing the threat with the police (or anyone else).

"This post is protected under international copyright agreements. Responding to, altering, deleting or modifying it is subject to investigation by the FBI and/or Interpol. Penalties may include upto five years imprisonment and $50,000 fines." (c) dbcisco,2009
There, that'll work.