Of course this is an email scam.
The best thing to do is to NEVER, EVER respond to scam or unsolicited commercial email. When you respond to the scammer or spammer you have just VALIDATED your email address as being "live," which makes your email address MORE VALUABLE. The scammer/spammer will then SELL your email address to others.
By responding with such nonsense as a number for an FBI office, you've just guaranteed that the scammer/spammer will get a higher price for selling your email address.
One thing that does work, at least temporarily, is to report the scammer/spammer to the ISP that is being used. All reputable ISPs will cutoff the offending account of a scammer/spammer. This is a temporary shut down of their operations because these bonzos simply switch to another ISP with a new account. Unfortunately, there are some ISPs that seem to support this type of operation and will not shut them down. If the ISP is based in china and a few other places, don't expect anything to be done about them.
Simply delete them or set your email client to filter them out, but NEVER RESPOND to such emails.