The ACLU recently released the FBI's "Domestic Investigations and Operations Guide" which states
"...On the other hand, if the contents of an unopened
message are kept beyond six months or stored on behalf of the customer after the e-mail
has been received or opened, it should he treated the same as a husiness record in the
hands of a third party, such as an accountant or attorney. In that case, the government
may subpoena the records from the third party without running afoul of either the Fourth
or Fifth Amendment."
our privacy rights should not change simply because the communication is older than 180 days. The US attorney for manhatten says a subpeona is "a piece of paper signed by a prosecutor, not a judge" and the IRS believes we have "generally no privacy" in email or chats.