Terms of Service.

By creating a StackSender account, calling the StackSender API, or otherwise using the Service, you agree to these Terms. If you are agreeing on behalf of a company, you confirm you have authority to bind it, and “you” means that company.

You must be at least 16 years old, and you must not be barred from receiving services under applicable export-control or sanctions law.

Our Privacy Policy is part of this agreement.

• Give accurate signup information and keep it current. Accounts created with falsified identity details may be terminated without notice.
• API keys are shown once at creation and stored by us only as an argon2 hash. Treat them like passwords: never commit them to a public repository, never ship them in client-side code. You are responsible for every request made with your keys. Rotate or revoke a key from the dashboard the moment you suspect exposure.
• We may require verification — including a payment method — before enabling or raising sending limits, particularly on the free tier. Free sending capacity is the most abused surface in this industry and we gate it accordingly.
• One account per organisation. Creating additional accounts to work around quotas, caps, or a suspension is itself a violation of these Terms.

Strictly prohibited

You may not use StackSender to send, facilitate, or assist with:

• Unsolicited bulk email (spam)of any kind, including “cold outreach” blasts to recipients who never asked to hear from you.
• Mail to purchased, rented, scraped, harvested, appended, or otherwise third-party-sourced lists. If you did not collect the address yourself with the recipient's consent, you may not mail it here. This includes lists compiled from web scraping, data brokers, conference attendee dumps, and public directories.
• Phishing and credential harvesting — including any message designed to impersonate a bank, employer, government agency, cloud provider, or other brand in order to collect passwords, payment details, one-time codes, or seed phrases.
• Malware — viruses, ransomware, spyware, trojans, malicious attachments, or links to any of the above.
• Forged or misleading headers — spoofed From or Reply-To identities, deceptive subject lines, or domains chosen to impersonate someone else.
• Fraud and financial abuse: advance-fee scams, fake invoices, pump-and-dump or unsolicited crypto promotion, pyramid and MLM recruitment, deceptive “you have won” offers.
• Illegal content, including material that sexually exploits minors, unlawful pornography, illegal drugs and controlled substances, illegal firearms, stolen data, counterfeit goods, or content that infringes another party's intellectual property.
• Harassment, threats, doxxing, or hate speech targeting individuals or protected groups.
• Mail to addresses on your suppression list, or to anyone who has unsubscribed, hard-bounced, or filed a spam complaint against you.
• Any attempt to defeat unsubscribe handling — hiding, disabling, or failing to honour opt-out mechanisms.
• Reselling StackSender capacity as a relay for third parties whose sending practices you cannot vouch for or evidence.
• Circumventing rate limits, quotas, plan caps, or suppression through technical means; probing or attacking the Service or its infrastructure; or attempting to access another customer's data.

Reporting abuse

If you receive spam or a phishing message sent through StackSender, forward it with full headers to support@stacksender.com. We investigate every report, suppress the reported address for that sender, and act on the account. Reports concerning security flaws should go to security@stacksender.com instead.

You warrant that every recipient you mail through StackSender has a genuine relationship with you and either requested the message or gave you permission to send it. Transactional messages — password resets, receipts, order updates, security alerts — are sent because the recipient took an action. Marketing and broadcast messages require documented opt-in.

• You must be able to produce evidence of consent — when, where, and how the address was collected — within 5 business days of our request. Inability to produce it is grounds for suspension.
• You are responsible for complying with the law that applies to you and your recipients, including the US CAN-SPAM Act, Canada's CASL, the GDPR and the ePrivacy Directive in the EU/UK, and any equivalent regime elsewhere.
• Bulk and marketing messages must identify you accurately, include a valid physical postal address where required, and carry a working unsubscribe mechanism. StackSender provides unsubscribe links, a hosted preference centre, and category-level opt-out for broadcasts — you must not remove or disable them.
• Unsubscribe requests must be honoured promptly. Our platform records them automatically; overriding that record by re-importing an unsubscribed address is a violation.
• You are responsible for the content of everything you send, including content generated by your own users or by automated systems on your behalf.

You may only send from domains you own or are authorised to use. Before a domain can send, you must add the DKIM, SPF, and DMARC-related DNS records we generate for it and pass verification. Sends from unverified domains are rejected by the API.

Registering a domain you do not control, or one chosen to impersonate another brand, is a termination-level violation. We may re-check verification at any time and disable a domain whose records have been removed or altered.

Plan limits apply to the number of sending domains per account (1 on Free, 3 on Starter, 10 on Pro, 100 on Scale, 1,000 on Volume).

Unless your plan includes a dedicated IP, your mail leaves over shared sending infrastructure. Your sending behaviour therefore affects every other customer, and theirs affects you. To protect the pool:

• Hard bounces and spam complaints are added to your suppression list automatically, and subsequent sends to those addresses are blocked.
• We monitor bounce and complaint rates continuously. Accounts whose combined bounce-and-complaint rate exceeds 5% over a rolling 24-hour window (on a meaningful volume of sends) are flagged for review and may be throttled or suspended.
• Per-team rate limits apply to the sending API, and free-tier accounts have a daily cap. Sustained attempts to exceed them are treated as abuse.
• We may refuse, delay, or throttle any message that we reasonably believe would damage the platform's reputation with receiving providers.

We do not guarantee that any particular message reaches any particular inbox. Inbox placement is decided by the receiving provider, not by us.

• Paid plans are monthly subscriptions in US dollars, billed in advance through Stripe, and renew automatically until cancelled.
• Overage. The monthly figure above is an included allowance, not a hard ceiling. Sends beyond it are metered and billed at $0.40 per 1,000 emails ($0.0004 per email) on the following invoice.
• The free plan is a hard stop. With no payment method on file there is nothing to bill overage against, so free accounts are capped rather than metered.
• Cost caps. You can set a monthly spend cap in the dashboard. We send alerts at 50%, 75%, and 90% of the cap, and at 100% we pause sending (the API returns HTTP 402) until you raise the cap or the calendar month rolls over. The cap window is the UTC calendar month, which will not always line up with your Stripe billing period.
• Prices exclude taxes. Where we are required to collect VAT, GST, or sales tax, it is added at checkout.
• Failed payments may result in suspension of sending until the balance is settled. We will email you before that happens.
• We may change prices with at least 30 days' notice by email. Changes take effect at your next renewal; if you do not accept them, cancel before that date.

• You can cancel at any time from the dashboard. Cancellation takes effect at the end of the current billing period; your plan stays active until then.
• Subscription fees are not refunded for partial months, and downgrades do not produce a prorated credit, except where local consumer law requires otherwise.
• Metered overage already accrued in the current period remains payable on the final invoice.
• If the Service materially failed on our side — a confirmed outage or a defect that prevented sending — email support@stacksender.com. We handle those case by case and would rather refund a bad month than argue about it.
• No refunds are issued for accounts terminated for violating the acceptable use policy.

• We may suspend or terminate an account immediately, without notice, for spam, phishing, malware, fraud, sending to non-consenting recipients, sustained abusive bounce or complaint rates, non-payment, or any attempt to circumvent these Terms.
• Where the violation looks accidental and the risk is contained, we will normally throttle first and contact you. Where it does not, we will not.
• We may report confirmed abuse to our upstream email provider, to receiving providers' abuse desks, and to law enforcement, and may share the account details relevant to that report.
• On termination your right to use the Service ends immediately. Export anything you need beforehand — after termination we delete account data on our normal retention schedule, described in the Privacy Policy.
• You may terminate at any time by cancelling and deleting your account.

The email you send, the contacts you upload, and the content of your messages remain yours. You grant us only the licence needed to operate the Service: transmitting, storing, rendering, logging, and reporting on that content, and processing it as your service provider.

You warrant that you have the rights and lawful basis for every address and every piece of personal data you push through the API. For that data we act as a processor and you act as the controller.

We may use aggregated, de-identified operational metrics — total volume, error rates, latency — to run and improve the platform. We do not read, sell, or mine your message content for any other purpose, and we do not use it to train models.

We work hard to keep the Service up, and the status page publishes live health checks. But we are honest about what we commit to:

• Free, Starter, and Pro plans are provided without an uptime guarantee and without service credits.
• Where a plan expressly includes an uptime commitment, that commitment and its credit mechanism are the sole remedy for downtime, and are calculated per calendar month excluding scheduled maintenance and events outside our control.
• We may modify, suspend, or discontinue features. For material removals affecting paid plans we will give reasonable advance notice.
• Beta and preview features are provided as-is and may change or disappear without notice.
• The Service depends on third-party infrastructure — notably our upstream email, database, hosting, queueing, and payment providers. Their outages will affect us, and are not something we can indemnify you against.

StackSender, its software, documentation, design, and marks are ours or our licensors'. These Terms grant you a limited, non-exclusive, non-transferable right to use the Service; they do not transfer ownership of anything.

You may not copy, reverse-engineer, or resell the Service, or use it to build a directly competing product. If you send us feedback or feature suggestions, we may use them without obligation to you.

To the maximum extent permitted by law, the Service is provided “as is” and “as available”, without warranties of any kind, whether express, implied, or statutory, including merchantability, fitness for a particular purpose, and non-infringement.

In particular, we do not warrant that mail will be delivered to any specific inbox, that it will avoid a recipient's spam folder, that the Service will be uninterrupted or error-free, or that any defect will be corrected within a particular time.

To the maximum extent permitted by law, neither party is liable for indirect, incidental, special, consequential, exemplary, or punitive damages, or for lost profits, lost revenue, lost data, or business interruption, even if advised of the possibility.

Our total aggregate liability arising out of or relating to the Service is limited to the greater of (a) the fees you paid us in the 12 months before the event giving rise to the claim, or (b) US $100.

Nothing here excludes liability that cannot lawfully be excluded — including liability for fraud, or for death or personal injury caused by negligence.

You will defend and indemnify StackSender against claims, damages, penalties, and reasonable legal costs arising from the messages you send, the data you upload, your breach of these Terms or of the acceptable use policy, or your violation of anti-spam, privacy, or other applicable law. That includes claims brought by your recipients and enforcement actions brought by regulators.

We may update these Terms as the Service evolves. The “last updated” date at the top reflects the current version. For material changes we will notify account holders by email before they take effect. Continuing to use the Service after that date means you accept the revised Terms.

• Entire agreement. These Terms and the Privacy Policy are the whole agreement between us regarding the Service.
• Severability. If a provision is unenforceable, the rest stays in force.
• No waiver. Not enforcing a provision once does not waive it.
• Assignment. You may not assign these Terms without our consent; we may assign them in connection with a merger, acquisition, or sale of assets.
• Governing law. These Terms are governed by the laws of the jurisdiction in which StackSender is established, without regard to conflict-of-laws rules, and the courts of that jurisdiction have exclusive jurisdiction over disputes — except that either party may seek injunctive relief wherever necessary to protect its intellectual property.
• Force majeure. Neither party is liable for delays caused by events beyond its reasonable control.

Questions about these Terms, billing, or an account action: support@stacksender.com

Security vulnerabilities: security@stacksender.com