The Two Lovers and the Necklace

Two people mike and angela are deeply in love but live very far apart. for her birthday mike wants to send angela a very valuable necklace but the posting system is very dodgy, the post service opens anything that can be opened or is seen to have value, packages can only be sent if they are locked because the posting people do not bother to open things that will involve time.

How can mike get his necklace to angela in a locked boxed when he can’t send her the keys of the lock because they will be confiscated?