Short answer. Through an affidavit of the person who mailed it, stating the facts showing compliance with the mail-service requirements, together with the registry receipt issued by the mailing office. The registry return card must then be filed as soon as received, or, if unclaimed, the returned letter with the postmaster's sworn or certified notice.
What the law says
If the service is made by: (a) Ordinary mail. – Proof shall consist of an affidavit of the person mailing stating the facts showing compliance with [S]ection 7 of this Rule. (b) Registered mail. – Proof shall be made by [ the] affidavit mentioned above and the registry receipt issued by the mailing office. The registry return card shall be filed immediately upon its receipt by the sender, or in lieu thereof[ ,] the unclaimed letter together with the certified or sworn copy of the notice given by the postmaster to the addressee.
Rule 13, Section 17 — Proof of service. Read the full provision →
General proof of service, then mode-specific detail
Proof of personal service can rest on a written admission from the party served, an official return from the server, or an affidavit stating the date, place, and manner of service. Where service is instead made by mail, however, this section adds specific documentary requirements layered on top of that general affidavit approach, tailored to the particular way the mail was sent.
For registered mail specifically
Proof consists of the affidavit of the person who mailed the pleading, together with the registry receipt issued by the mailing office at the time of sending. That affidavit needs to state facts showing the mailing complied with the registered-mail service requirements elsewhere in this Rule — the sealed envelope, correct addressing, prepaid postage, and the postmaster's return instruction all need to be reflected there.
The follow-up step: the registry return card
Proof of registered mail service does not stop at the initial receipt from mailing. The registry return card — the slip that comes back once the addressee, or someone else at that address, signs for the mail — must be filed immediately upon the sender receiving it back from the postal service. If the letter instead goes unclaimed entirely, the sender files the unclaimed letter itself along with a certified or sworn copy of the notice the postmaster gave to the addressee about it.
Why two stages of proof exist
Requiring both the initial registry receipt and the later return card, or unclaimed-letter documentation, reflects the two-step nature of registered mail itself: mailing is one discrete event, and actual delivery or non-delivery is another event entirely, discovered only afterward once the postal process has run its course. The rule tracks both stages so the court eventually has a complete record of what was sent and what ultimately happened to it.
Related provisions
- Rule 13, Section 17 — Proof of service
- Rule 13, Section 16 — Proof of filing
- Rule 13, Section 18 — Court