(a) If, on examination, it appears that the applicant is entitled to a patent under the law, a notice of allowance will be sent to the applicant atthe correspondence address indicated in § 1.33. The notice of allowance shall specify a sum constituting the issue fee and any required publication fee (§ 1.211(e)), which issue fee and any required publication fee must both be paid within three months from the date of mailing of the notice of allowance to avoid abandonment of the application. This three-month period is not extendable.