Padded envelop through USPS.
Here is their postage calculator
http://postcalc.usps.com/
Send it standard package with a tracking label. Make sure you put it in a very strong box so it doesn't get damaged. If it's an expensive necklace get insured package. It will cover any costs if the item is damaged.
A thick yellow envelope
length isn't the issue weight is. check upps economy and ups. know total weight boxed or not
