Two ways to send a signed page
For decades the fax was how a signed document moved between two offices, and in plenty of industries it still is — print the contract, sign it by hand, feed it through a machine, and trust that the page that comes out the other end is the page you sent. It works, in the sense that documents get signed. But "it works" and "it proves what happened" are different claims, and that gap is the whole story when you compare a fax to an electronic signature.
This is a plain comparison of the two for getting a document signed and agreed: what each one actually proves, how they differ on legality, speed, and cost, and where a fax still has a narrow place.
Are both legally valid?
Yes — and this surprises people who assume one is "more official." A handwritten signature on a faxed page is a valid signature; the fax is just a transmission method. An electronic signature is also valid, under ESIGN and UETA in the US and eIDAS in Europe, which give an electronic signature the same legal standing as ink on paper for the large majority of business documents.
So legality isn't the dividing line. Both can produce an agreement a court will honor. The real difference shows up the moment someone questions the agreement — because then you're not arguing about validity in the abstract, you're producing proof of what happened. And that's where the two diverge sharply, the same way a wet signature and an electronic signature diverge on the strength of the record behind them.
What each one actually proves
A fax proves remarkably little about the event of signing. The page shows a signature, and the fax header shows a sending number and a timestamp from the sending machine — both of which are trivially spoofable and tell you nothing about who held the pen or whether the page was altered before it was sent. There's no tamper-evidence: a faxed page can be edited, re-printed, and re-faxed, and the result looks identical. If a signer later claims "that's not the version I signed," a fax gives you almost nothing to push back with.
An e-signature is built to answer exactly those questions. The signature is tied to a verified email, IP address, device, and per-step timestamps, all recorded in an audit trail that holds up. The final document is sealed with a SHA-256 hash and an RFC 3161 trusted timestamp, so any later change to a single character is detectable and provable. Where a fax leaves you with a page, an e-signature leaves you with an independently verifiable evidence bundle — the difference between "here's a signed copy" and "here's proof of who signed, when, and that nothing changed since."
Speed and friction
A fax requires both sides to have a working fax line or service, the signer to print and physically sign, and someone to feed and confirm each transmission. Multi-party documents become a relay: sign, fax, receive, sign again, fax back. An e-signature collapses that into a link — the signer opens, signs on any device including their phone, and the next party is notified automatically through the routing order you set. For anything beyond one signer and one page, the time difference is dramatic, which is the core of reducing contract turnaround time.
Cost and operations
Faxing carries hidden operating cost: hardware or a per-page fax service, paper and toner, and the staff time to babysit transmissions and chase failed sends. There's also no central record — signed faxes live in inboxes, drawers, and scanned PDFs, with no consistent place to search or retain them on a schedule. E-signing replaces all of that with a credit-based or flat per-document cost and a searchable record where every signed document and its certificate live together.
Where a fax still has a place
Honesty matters here: a fax isn't useless. A handful of agencies, courts, and older institutional workflows still require fax submission or won't accept anything else, and when that's the rule, a fax is what you send. But that's a counterparty constraint, not a reason to prefer fax for your own signing — and even then, you can sign electronically, export the sealed PDF, and fax that, keeping the strong record on your side of the exchange.
The takeaway
A fax and an e-signature can both produce a legally valid signed document, so legality isn't the deciding factor. The deciding factor is proof: a fax leaves you a page with a spoofable header and no tamper-evidence, while an e-signature leaves you a tied audit trail, a SHA-256-sealed, timestamped evidence bundle, and a searchable record — plus it's faster and cheaper for anything past a single signer. Send the fax when a counterparty demands one; for everything you control, sign electronically and keep the proof. Start free or see the features.
This article is general guidance, not legal advice. For document-format requirements specific to your industry or jurisdiction, consult qualified counsel or a compliance specialist.