0 missed billing emails across 40,000 developers — 14 months and counting
How Mintlify built an email infrastructure as reliable as the documentation platform it powers
Mintlify serves 40,000 developers whose docs sites live on their platform. Missing a deploy failure alert means a developer's product is broken without them knowing. Missing a payment failure email means involuntary churn. Neither is acceptable.
Mintlify is the documentation platform for developer-facing products. Their customers — developer tools companies, API providers, open-source projects — trust Mintlify to host and serve their documentation. That trust extends to email. When a deploy fails, the developer must know. When a payment method expires, the team must be notified before their docs site goes offline. When a collaborator joins a workspace, the confirmation must arrive instantly. These aren't marketing emails. They're operational signals.
The challenge
Zero tolerance for missed billing emails
A missed payment failure notification means a developer's docs site eventually goes offline — and the developer doesn't know why, because they never got the warning. Mintlify measured their previous provider's billing email delivery rate at 97.3%. At 40,000 developers, that 2.7% failure rate translated to over 1,000 developers per billing cycle who didn't receive critical payment warnings. Each one was a potential involuntary churn.
No audit trail for high-stakes sends
When a developer contacted support saying they hadn't received their invoice, Mintlify had no way to verify whether the email was sent, when it was sent, or why it might have failed. They were taking developers at their word — and in cases where payment information was disputed, "we sent the email" without proof wasn't a satisfying answer for either side.
Deploy alerts with latency that defeated their purpose
Deploy failure alerts sent with a 3–5 minute lag meant developers were already investigating issues before the email arrived — or had already closed the tab and missed the window to respond quickly. The alert was confirmation, not notification.
The solution
Mintlify migrated all four critical email flows to Sendbound: deploy alerts, payment failure warnings, invoice delivery, and workspace invitations. For each send, they implemented a webhook consumer that writes a delivery receipt — including SMTP response codes, timestamps, and recipient-domain data — to their Postgres database. Every email now has a full audit trail. Deploy alerts fire within seconds of the triggering event. Billing email delivery has been at 100% for fourteen months.
import Sendbound from '@sendbound/sdk';
const sb = new Sendbound({ apiKey: process.env.SENDBOUND_API_KEY });
export async function sendDeployFailureAlert(deploy: Deploy) {
const { id, accepted } = await sb.emails.send({
from: 'Mintlify Alerts <alerts@mintlify.com>',
to: deploy.team.notificationEmail,
subject: `Deploy failed: ${deploy.projectName}`,
template: 'deploy-failure',
variables: {
project_name: deploy.projectName,
branch: deploy.branch,
error_summary: deploy.errorSummary,
logs_url: deploy.logsUrl,
triggered_by: deploy.triggeredBy,
},
tags: ['deploy-alert', `project:${deploy.projectId}`],
});
// Write delivery receipt to our audit DB
await db.emailAudit.create({
data: { emailId: id, accepted, deployId: deploy.id,
recipientEmail: deploy.team.notificationEmail },
});
}
// Webhook handler updates the audit record with full delivery event"We have 40,000 developers who need to know when something goes wrong with their deploy or their billing. Sendbound is the layer we trust with that responsibility. It has never let us down in fourteen months of production. For infrastructure that this important, "never" is the only acceptable answer."
The impact
The "I never got the email" support category, which had accounted for roughly 8% of Mintlify's support volume, dropped to near zero within a month of migration. More importantly, Mintlify now treats email delivery as a first-class system observable — it appears on their internal reliability dashboard alongside uptime, latency, and error rates. Their developers-as-customers see email reliability as part of Mintlify's overall reliability story.
Results at a glance
- 0 missed billing emails across 40,000 developers — 14 months running
- Deploy failure alerts firing in seconds, not minutes
- 100% audit trail coverage — every send has a delivery receipt in Postgres
- "I never got the email" support tickets dropped by ~90% in month one
- Email reliability now a first-class metric on Mintlify's internal dashboard
- Involuntary churn from missed payment warnings eliminated
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