Signing completion rate up 22% — without changing a word of copy
How Zignature turned email deliverability into a competitive advantage in the e-signature market
In e-signature, a document request that hits spam is a deal that doesn't close. Zignature processes 180,000 signing invitations per month across legal, real estate, and HR. They thought their completion problem was UX. It was deliverability.
Zignature handles electronic signatures for law firms, real estate agencies, HR departments, and finance teams. Their platform sends 180,000 signing invitations per month — requests for people to review and sign legally binding documents. The entire business model depends on those emails arriving, being opened, and driving action. A document request that lands in spam doesn't get signed. Deals stall. Renewals don't close. Employees don't onboard.
The challenge
A completion problem disguised as a UX problem
Zignature had been running A/B tests on their invitation email for a year. Subject line variations, send-time optimization, personalization tokens, button copy. Nothing moved the needle beyond a point or two. When they finally instrumented delivery rates at the recipient-domain level, they found that 11% of invitations to enterprise email domains — Outlook, corporate Exchange servers — were being filtered to spam. The completion rate "problem" was never a conversion problem. It was a delivery problem.
Per-sender-domain authentication at scale
Zignature sends on behalf of their customers — a law firm's invitation arrives from the firm's domain, not Zignature's. Managing DKIM signing keys for hundreds of customer domains on their previous provider required a manual UI workflow per domain. As they grew, this became a significant operational bottleneck.
Latency variance that broke time-sensitive flows
Some enterprise signing workflows are time-gated — a contract must be signed within 24 hours or it expires. Their previous provider's P99 delivery latency was measured in minutes, occasionally longer. For high-stakes documents, that variance was unacceptable.
The solution
Zignature migrated to Sendbound in two phases. First, they ported their own transactional flows (notifications, billing, alerts) to validate the platform. Then they built a per-customer DKIM provisioning system using Sendbound's domain API — each customer domain gets its own signing key, managed programmatically. Within two weeks, all 180,000 monthly invitations were flowing through Sendbound with per-sender authentication. P99 delivery latency dropped to under 2 seconds. Inbox placement at enterprise domains went from 89% to 99.1%.
import Sendbound from '@sendbound/sdk';
const sb = new Sendbound({ apiKey: process.env.SENDBOUND_API_KEY });
// Programmatically provision DKIM for each customer domain
const domain = await sb.domains.create({
domain: customer.signingDomain, // e.g. "contracts.acmecorp.com"
returnPath: `return.${customer.signingDomain}`,
});
// DNS records to give the customer for their registrar
const { dkim, spf, returnPath } = domain.dnsRecords;
// Send invitation signed from the customer's own domain
await sb.emails.send({
from: `${customer.name} <contracts@${customer.signingDomain}>`,
to: signer.email,
subject: `Action required: ${document.title}`,
template: 'signing-invitation',
variables: { signer_name: signer.name, sign_url: document.signUrl },
});"We thought our completion rate problem was a UX problem. We ran experiments for a year. Turned out it was a deliverability problem the whole time. Sendbound fixed it before we even had to A/B test anything. Twenty-two percent improvement in signing completion — from infrastructure. That still doesn't feel real."
The impact
Signing completion rate climbed 22% in 60 days without any changes to the invitation email content, UX, or send-time strategy. The entire lift came from emails arriving in inboxes instead of spam folders. Zignature's CEO called it the highest-ROI infrastructure decision they've made: one sprint of migration work, 22 points of completion rate, zero ongoing maintenance.
Results at a glance
- Signing completion rate up 22% in 60 days — no copy or UX changes
- Enterprise inbox placement (Outlook, Exchange) from 89% to 99.1%
- P99 delivery latency from minutes to under 2 seconds
- Per-customer DKIM provisioning fully automated via API
- Zero manual domain configuration work since migration
- A/B testing budget redirected to actual product improvements
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