How do I stop someone else from signing using a landlord's email?

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This is an unsettling situation to land in, because it means the signed agreement you were relying on might not actually be what it appears to be. Before anything else, slow down rather than assuming the worst or dismissing it. Figure out what the landlord is actually claiming, that their email was hacked, that someone with legitimate access (a property manager, a family member) signed on their behalf without clear authorization, or that they're disputing a signature they genuinely did make. Each of those is a different problem with a different fix.

It's also worth considering, calmly, whether the landlord's claim is itself accurate. People sometimes genuinely forget signing something, especially weeks or months later, or realize after the fact that they don't like the deal and look for a reason to back out of it. That's not an accusation to lead with, but it's a real possibility alongside the possibility that something actually did go wrong with access to their email. Treating the claim as worth investigating, rather than either automatically accepting or automatically dismissing it, is the right starting posture either way.

The no-tool way: paper, email or a phone call

A paper original signed in person avoids this specific problem entirely, since you're watching the actual person sign. For a deal already done remotely, the honest first step with no special tool at all is simply calling the landlord on a number you can independently verify, not one from the disputed email thread, and asking them directly whether they signed it. That single call often resolves more of this than any technical investigation will. If a customer or owner denies signing at all, what to do when a customer says they never signed the contract covers that dispute.

Where you get that verified number matters more than it sounds like it should. Pull it from your own prior records, an earlier contract, a business card, a previous phone conversation logged somewhere, rather than anything in the email thread currently in question, since if that thread or account really has been compromised, any contact details sitting inside it are compromised along with it.

The software options, from simple to most capable

DocuSeal

DocuSeal, an open-source e-signature tool available self-hosted for free or as a paid cloud product, includes SMS and OTP verification on its Pro cloud plan at $20 a user a month, with 20 verifications included monthly and $0.20 each after that. Its free Basic tier doesn't include this, and ID verification specifically isn't listed as included on either its cloud or on-premises plans.

DocuSign

DocuSign, one of the longest-running e-signature platforms, offers identity verification starting on its Standard plan at $30 a user a month, which includes a one-time bonus of 5 identity verifications, and more advanced authentication options are available on its custom Enhanced plans. This is one of the few options on this list that moves toward an actual identity check, not just a phone code. Tools built for property managers are compared in DocuSign alternatives for real estate and property management.

QuickSigner

QuickSigner is an electronic signature tool: upload a document, place signature fields, and send a secure link that works from any device, no account required for the signer. On its Professional plan, $15 a user a month (20% cheaper billed annually), it adds a one-time code sent to the signer's phone before they can complete signing. I found nothing stated anywhere on its site about government ID verification as a feature, so for this specific need, confirm directly with QuickSigner's support or look at a tool that explicitly advertises it, like DocuSign's identity verification add-on. Confirm current pricing on QuickSigner's own site.

Step by step: what to actually do

1. Confirm the signer by phone before sending anything, on a number you've independently verified, not one taken from the email thread itself, since that thread is exactly what's in question.
2. Add a phone code step if your tool offers it, as a standing practice for anything involving a landlord or property owner signing remotely, not just after a problem's already happened once.
3. Use a dedicated identity verification tool for anything requiring a real government ID check. None of the general e-signature tools covered here beyond DocuSign's add-on advertise this clearly, so don't assume a phone code or email confirmation substitutes for it if that's genuinely what you need.
4. Keep the full signing record, the audit trail, IP address and timestamp, since that's your actual evidence if this dispute goes further, not the final signed PDF alone.

When this is a legal problem, not just a technical one

If a landlord credibly claims someone else used their email to sign a lease, a listing agreement, or any binding document, that's not something a signing tool's audit trail alone resolves. Whether the agreement is still valid, voidable, or needs to be redone from scratch depends on the specific facts and your jurisdiction's contract law, which is a question for a lawyer, not something to settle by technical investigation alone, however good the audit trail is. The audit trail helps establish the facts, when, from what IP address, from what device, but what those facts legally mean for the agreement's validity needs a lawyer's read, especially if real money or a tenancy is on the line. The levels of proof available are compared in how to prove who signed.

This is also exactly the kind of situation where moving fast to "just fix it and move on" can make things worse rather than better. If you quietly send a replacement signing link and get a fresh signature without first understanding what actually happened the first time, you may have papered over a genuine problem, an account compromise, an unauthorized signer, that could resurface later in a worse form. Pausing to actually understand the facts before acting costs a day or two. Acting first and understanding later can cost considerably more if the original problem turns out to be bigger than a simple mix-up.

How I'd approach this

I'd treat a single incident like this as a signal to change the standing process, not just resolve the one dispute. If a property management company has had even one instance of a disputed signature tied to email access, I'd add a phone verification call as a required step before any signing link goes out, for every landlord, every time, not as a reaction to the one bad case but as a permanent part of the workflow. The actual cost of that extra step is a few minutes per deal. The setup is described in adding a phone code check before someone signs a high-value deal.

Picture a property management company handling thirty landlord-side agreements a year, lease renewals, listing authorizations, fee agreements. If a verification call before sending each one adds five minutes per deal, that's two and a half hours of staff time across the whole year. Compare that to the cost of even one disputed signature: the staff time spent investigating it, the potential legal cost of confirming the agreement's validity, and the damage to the relationship with that landlord if the dispute turns genuinely adversarial. Two and a half hours a year is a trivial price for avoiding even one incident anywhere close to that scale, and that's before counting the reputational cost of a landlord telling other owners in the area that your agency let something like this happen. I build this kind of standing verification step into client workflows specifically because it's cheap insurance that's easy to skip when nothing's gone wrong yet.