How to Prove You Sent a File on a Specific Date

Published by DocProof — July 7, 2026 — 4 min read

A client claims you delivered the wrong version. A contractor says they never received the brief. A partner disputes the terms you sent them last month. In each case, you need to prove not just what you sent, but when you sent it — and that it hasn't changed since.

Email read receipts can be disabled. Email timestamps can be disputed. Cloud storage timestamps can be modified. What you need is a cryptographic record that exists independently of any platform.

Why Email Isn't Enough

Email provides a rough timestamp, but it has serious weaknesses as proof:

• Email headers can be spoofed or altered
• The email server's clock can be wrong or manipulated
• The attachment in the email can be disputed — "that's not the file I received"
• Read receipts only confirm the email was opened, not that a specific attachment was received

In a dispute, a counterparty can raise doubts about any of these points. A cryptographic proof eliminates that ambiguity.

The Right Way to Prove File Delivery

The approach has two parts: timestamp the file before you send it, then keep a record of the send.

Step 1 — Timestamp the file before sending

Before you attach the file to an email or upload it to a shared folder, create a cryptographic proof of it. This records the SHA-256 fingerprint of the exact file alongside a UTC timestamp.

This proves:

• The file existed in that exact state at that moment
• The file you sent is identical to the file that was timestamped
• No one — including you — could have altered it after the timestamp without the fingerprint changing

Step 2 — Send and keep records

After timestamping, send the file normally. Keep:

• The DocProof certificate (PDF with the fingerprint, timestamp, and Proof ID)
• A copy of the sent email or upload confirmation
• The original file

If a dispute arises, anyone can take the file, hash it, and compare it to the certificate. If the fingerprints match, the file is identical to what was timestamped — and it existed before the dispute.

Practical Example

You send a design mockup to a client on July 7. Three weeks later, they claim you delivered something different from what was agreed. You:

1. Show the DocProof certificate dated July 7, with the SHA-256 fingerprint of the mockup.
2. Ask them to hash the file you sent (using DocProof's free SHA-256 tool).
3. The fingerprints match — proving the file they received is identical to the one you timestamped on July 7.

Dispute resolved. No he-said-she-said.

When This Matters Most

• Delivering work to clients as a freelancer or agency
• Sending contracts or proposals before negotiation
• Submitting documents to a regulatory body or court
• Handing off code or assets to a contractor
• Any situation where "I sent X on date Y" matters