If the Postal Service confirms that it incorrectly charged the mailer a fee that was less than the amount required to pay for the insurance coverage requested at the time of mailing, the mailer may pay the difference in order to receive the full indemnity available if the Postal Service had charged the correct fee. The Postal Service may pay the indemnity within the limit fixed for the higher fee; this applies only to the insurance fee when the article is insured. The mailer may not pay an additional fee to register an article previously sent by insured mail, or to increase the declared value on a Registered Mail article. The declared value must already be noted on the appropriate Registered Mail receipt: PS Form 3806, Receipt for Registered Mail; PS Form 3813, Insured Mail Receipt — Domestic Only — $500 and Under; or PS Form 3813-P, Insured Mail Receipt — Domestic Only — Over $500. The mailer must complete all entries on the current edition of PS Form 3877, Firm Mailing Book for Accountable Mail (or facsimile).
