content: It does have legal standing: a snooper cannot claim there was no way to know the email was non-public. The snooper will probably use an accidental disclosure defense in their first interview, which contradicts the written notice they were given. This tarnishes their credibility and can easily cost them the legal case. (The standard in civil court is preponderance of the evidence, so even a little loss of credibility is crippling.) P.S. This is why we never talk to the police or other people's lawyers. Admit nothing, deny everything, demand proof.