37 CFR 2.197 - Certificate of mailing or transmission.
(a) Except in the cases enumerated in paragraph (a)(2) of this section, correspondence required to be filed in the Office within a set period of time will be considered as being timely filed if the procedure described in this section is followed. The actual date of receipt will be used for all other purposes.
(1) Correspondence will be considered as being timely filed if:
(i) The correspondence is mailed or transmitted prior to expiration of the set period of time by being:
(A) Addressed as set out in § 2.190 and deposited with the U.S. Postal Service with sufficient postage as first class mail; or
(ii) The correspondence includes a certificate for each piece of correspondence stating the date of deposit or transmission. The person signing the certificate should have a reasonable basis to expect that the correspondence would be mailed or transmitted on or before the date indicated.
(2) The procedure described in paragraph (a)(1) of this section does not apply to:
(b) In the event that correspondence is considered timely filed by being mailed or transmitted in accordance with paragraph (a) of this section, but not received in the Office, and an application is abandoned, a registration is cancelled or expired, or a proceeding is dismissed, terminated, or decided with prejudice, the correspondence will be considered timely if the party who forwarded such correspondence:
(2) Supplies an additional copy of the previously mailed or transmitted correspondence and certificate; and
(3) Includes a statement that attests on a personal knowledge basis or to the satisfaction of the Director to the previous timely mailing or transmission. If the correspondence was sent by facsimile transmission, a copy of the sending unit's report confirming transmission may be used to support this statement.
(c) The Office may require additional evidence to determine whether the correspondence was timely filed.