Recipient's signature: refers to the signature of the person who received your email, which may be the recipient or the salesperson.

Inspection: refers to the postal department's requirement that all mails must be inspected to distinguish whether they are illegally received or sent, that is, the signature of the person in charge of inspection.

Recipient's signature: it is the signature when the mail is received.

And the sender's signature: that is, the sender's signature.