Short answer. Through the registry receipt from the mailing, together with an affidavit of the person who mailed it stating the full date and place of deposit, that it was in a sealed envelope addressed to the court with postage fully prepaid, and that the postmaster was instructed to return it after ten days if undelivered.

What the law says

If the pleading or any other court submission was filed by registered mail, the filing shall be proven by the registry receipt and by the affidavit of the person who mailed it , containing a full statement of the date and place of deposit of the mail in the post office in a sealed envelope addressed to the court, with postage fully prepaid, and with instructions to the postmaster to return the mail to the sender after ten calendar days if not delivered.

Rule 13, Section 16 — Proof of filing. Read the full provision →

The baseline rule on proof of filing

Filing is generally proven simply by the pleading's existence in the case record, which is the default and easiest way to establish that a document was actually filed. But this section anticipates situations where the submission is not, or not yet, reflected in the record, and sets out mode-specific ways to still prove that filing genuinely happened. For a pleading filed by registered mail, two things together do that proving.

The two required pieces

First is the registry receipt issued at the time of mailing, obtained directly from the post office. Second is the affidavit of the person who actually mailed the pleading, and that affidavit is not meant to be a bare statement — it must give a full account of the date and place the mail was deposited at the post office, confirm it was in a sealed envelope addressed to the court, confirm postage was fully prepaid, and confirm the postmaster was instructed to return the mail after ten calendar days if it was not delivered.

Why both documents are required together

The registry receipt alone shows only that something was mailed to some address on some date; it does not by itself establish that the envelope actually contained the pleading in question or was properly addressed to the court in the form the rule requires. The affidavit fills in those missing details, and together the two documents reconstruct, after the fact, what the case record does not yet independently show on its own.

What this means in practice

A party who mailed a pleading and is later asked to prove it was filed on time should be ready to produce both the registry receipt and a sworn affidavit covering these specific details described above — not merely a simple assertion that the pleading was sent, but the concrete, verifiable facts of the actual deposit itself at the post office.

Related provisions

Note. Statute text quoted on this page is reproduced from the official enactment and is linked to the full provision. The explanation around it is general legal information from Vivas & Nobles Law Office, not legal advice. Whether it applies to your situation depends on facts only a lawyer reviewing them can assess.