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Terms of Service

Last updated: May 5, 2026

These Terms of Service ("Terms") govern your use of the Postlark email verification API and the website at postlark.io (collectively, the "Service"), provided by Horizon Analytic Studios, LLC ("we," "us," or "our"). By creating an account or using the Service, you agree to these Terms.

Account Registration

You must provide a valid email address and confirm it before using paid features. You are responsible for keeping your account credentials and API keys secure. You are responsible for all activity under your account, including activity initiated by anyone you grant access to.

You must be at least 13 years old to use the Service. If you are creating an account on behalf of an organization, you represent that you have authority to bind that organization to these Terms.

The Service

Postlark accepts an email address and returns a structured verdict — syntax, MX, disposable detection, role-account detection, free-provider detection, typo suggestions, and (where available) SMTP reachability. The Service is provided "as is"; verification verdicts are best-effort signals derived from public DNS data and heuristics, not guarantees of email deliverability or recipient identity.

Acceptable Use

You agree not to use the Service to:

  • Verify lists you do not have permission to process (purchased lists, scraped contacts, or addresses obtained without consent).
  • Send unsolicited bulk email or otherwise violate anti-spam laws (CAN-SPAM, CASL, GDPR, etc.).
  • Probe, scan, or test the vulnerability of any system or network not owned by you.
  • Circumvent rate limits, quotas, or other technical restrictions.
  • Resell or repackage the Service without a written agreement.
  • Use the Service to harass, defame, or impersonate others.

We may suspend or terminate accounts that violate these rules, and we reserve the right to refuse service to anyone for any lawful reason.

Plans, Billing, and Quotas

The Service offers a free tier (100 verifications/month) and paid subscription tiers. Paid plans renew monthly via Stripe. Plan quotas reset at the start of each billing period; verifications beyond your quota are billed at your plan's overage rate (paid plans) or rejected with a 429 response (free plan).

You may upgrade, downgrade, or cancel your subscription at any time from the dashboard. Cancellation takes effect at the end of your current billing period; you retain access to paid features until then. We do not provide refunds for partial periods unless required by law.

We may change plan pricing or quotas; we'll provide at least 30 days' notice via email before any change affects your account.

API Keys

API keys authenticate your requests to the Service. You are responsible for safeguarding your keys and for any usage they incur. If you suspect a key has been compromised, revoke it immediately from the dashboard. Revoked keys cannot be reactivated; issue a new key.

Your Data

You retain ownership of all email addresses and other data you submit to the Service. You grant us a limited license to process that data solely for the purpose of providing the Service. See our Privacy Policy for details on how we handle your data.

Intellectual Property

The Postlark name, logo, website, and software are the property of Horizon Analytic Studios, LLC and are protected by intellectual-property laws. These Terms grant you no rights to our trademarks, logos, or branding.

Service Availability

We aim to keep the Service available and working correctly, but we do not guarantee uninterrupted availability. We may perform scheduled maintenance, deploy updates, or experience unplanned downtime. Service-level commitments, where offered, are documented separately for paid plans.

Disclaimer of Warranties

The Service is provided "as is" and "as available," without warranties of any kind, express or implied, including (without limitation) merchantability, fitness for a particular purpose, and non-infringement. Verification verdicts are signals, not guarantees; you should not rely solely on Postlark to determine whether to send email to a given address.

Limitation of Liability

To the maximum extent permitted by law, Horizon Analytic Studios, LLC's total liability arising out of or relating to the Service shall not exceed the amount you paid us in the 12 months preceding the event giving rise to the claim. We are not liable for any indirect, incidental, special, consequential, or punitive damages, or for lost profits, revenue, or data.

Indemnification

You agree to indemnify and hold harmless Horizon Analytic Studios, LLC and its affiliates from any claims arising from your use of the Service in violation of these Terms or applicable law.

Termination

You may close your account at any time from the dashboard. We may suspend or terminate your access for material breach of these Terms or for non-payment. On termination, your right to use the Service ends and your data may be deleted as described in our Privacy Policy.

Governing Law

These Terms are governed by the laws of the State of Texas, without regard to its conflict-of-law provisions. Any dispute arising under these Terms shall be resolved in the state or federal courts located in Texas, and you consent to the personal jurisdiction of those courts.

Changes

We may modify these Terms from time to time. Material changes will be communicated via email and reflected in the "Last updated" date above. Continued use of the Service after changes take effect constitutes acceptance of the modified Terms.

Contact

For questions about these Terms, contact us at info@postlark.io or via our contact form.