Terms of service

These terms apply to the use of Letterpier by businesses within the meaning of § 14 BGB, legal entities under public law and special funds under public law. Letterpier is not offered to consumers. By accepting these terms, the customer confirms that it acts as a business.

Letterpier is operated by Michael Ketzer, Rotkehlchenweg 51, 40789 Monheim am Rhein, Germany (“we”, “us”). Our full contact details are in the legal notice.

The customer’s own general terms do not apply, even if we do not object to them, unless we agree to them in text form.

In these terms:

Customer

The business that has concluded the contract with us, including the people it allows to use its organisation.

Service

Letterpier, as described in § 3.

Organisation and project

An organisation is the customer’s account. It holds projects: isolated workspaces with their own API keys, domains, webhooks, messages and suppression list.

Customer data

All data that the customer, or mail servers sending to the customer’s domains, transmit to the service, including messages, attachments, events and configuration.

Text form

A readable declaration on a durable medium within the meaning of § 126b BGB, for example an email.

There is no public registration. Access is granted on request and at our discretion. The contract is concluded when we confirm acceptance in text form. [For legal review: alternatively: when we activate the customer’s organisation]

Before we activate the customer’s organisation, we send these terms and the data processing agreement in text form. The customer accepts them by confirming in text form. With our confirmation, we send the accepted versions or links to their archived versions. [For legal review: acceptance by confirmation in text form before activation; a click-through acceptance in the request-access form would be an alternative (owner decision)]

Before we grant access, we check by hand that the requester is a business. We may ask for evidence, for example an extract from the commercial register or a VAT identification number.

These terms can be retrieved and stored at any time at app.letterpier.com/legal/terms, for example with the “Print or save as PDF” button on this page. Earlier versions remain available in the version history at the end of this page.

The contract language is English.

Letterpier sends and receives transactional email for the customer’s own products. The service consists of:

1. a Resend-compatible HTTP API, tested with the unmodified resend@6.30.0 Node SDK using baseUrl. Letterpier does not offer complete Resend parity. Unsupported operations return an explicit error. The compatibility table at /docs/compatibility is part of the service description;
2. live sending through Postal, the mail server software we operate. Sandbox messages are captured, never delivered, and produce synthetic events;
3. catch-all receiving on verified domains;
4. webhooks in the Svix format, delivered at least once, with up to 8 attempts (after 5 s, 5 min, 30 min, 2 h, 5 h, 10 h and 10 h). The customer deduplicates on svix-id;
5. a dashboard for organisations, projects, domains, API keys, webhooks, suppressions and message logs.

The following limits apply:

Recipients per message

50 (to, cc and bcc together)

Attachments per message

20

Attachment size

About 10 MB in total per request

Text and HTML body

250,000 characters each

Batch requests

Up to 100 messages, accepted atomically (all or none)

Scheduled sending

Up to 30 days ahead

Idempotency keys

Honoured for 24 hours

API requests

100 per minute per project and environment

Live sending

Initially 1,000 messages per hour per project; we may adjust this limit per project

The customer chooses how long message content is kept, from 1 to 90 days per project (30 days by default). After that period, messages, their content, attachments and events are deleted automatically. Letterpier is not an archive.

“Delivered” means that a receiving mail server accepted the message. We do not guarantee placement in any inbox.

Features that our website or documentation describes as “not yet available” are not part of the service.

During the developer preview, Letterpier is provided without a committed availability level and without committed support response times. Maintenance may cause interruptions; the application and Postal pause briefly each night while backups are staged (around 03:15 UTC). Features may change.

Letterpier runs on a single server. If that server fails, sending, receiving and the dashboard are unavailable until it is restored.

[For legal review: written as a service description, not as an exclusion; courts may treat availability disclaimers as disguised limits of liability]

The customer shall:

1. comply with the acceptable use policy and the law, in particular § 7 UWG and the GDPR, and have a lawful basis for every message it sends;
2. send only from domains it holds the rights to;
3. keep its DNS records correct. Receiving requires the domain’s MX record to point to Letterpier, so the customer uses a dedicated subdomain if existing mailboxes would be affected by the change;
4. keep API keys secret, use them only on servers, and revoke a key immediately if it may be exposed;
5. secure its webhook endpoints: public HTTPS on port 443 with a valid TLS certificate and no redirects. The customer verifies the signature of every webhook;
6. treat received messages and attachments as untrusted. No antivirus scanning of attachments is configured;
7. keep the email accounts used to sign in secure, because sign-in codes are sent there;
8. keep its own copies of any data it needs to keep;
9. not send special categories of personal data (Article 9 GDPR) unless we have agreed to this in text form. [For legal review: policy choice for the operator]

The customer is responsible for the content of its messages.

The data processing agreement at /legal/dpa forms part of this contract.

Where we process personal data for our own purposes, for example to sign people in, the privacy policy applies.

Fees: free of charge during the developer preview.

Unless stated otherwise, prices are net and do not include the statutory value added tax.

We may offer changed prices in text form at least 6 weeks before they are to apply. They apply only if the customer agrees (§ 11). If the customer does not agree, either party may terminate the contract with effect from that date.

We may suspend or restrict access, in whole or in part, where this is necessary because of a breach of the acceptable use policy, a security risk, a legal order, or a threat to deliverability or to the reputation of shared sending infrastructure. We act proportionately, notify the customer in advance where possible, and give reasons.

In an incident we can stop all live sending at once (an emergency stop). This affects every customer, not only the one that caused the incident. While live sending is stopped, new live sending requests are rejected with an error, and messages we have already accepted stay queued. Messages already handed to the mail server may still be delivered unless we also pause it, which also delays receiving.

We lift a suspension as soon as its reason no longer applies. Our right to terminate for cause is not affected.

[For legal review: statements of reasons under Article 14(4) DSA and, if the hosting classification applies, Article 17 DSA]

What the customer may send and receive through Letterpier is restricted by the acceptable use policy, which forms part of these terms.

We use these measures and tools to enforce it:

• domain verification: we send only from domains that prove ownership with a DNS record and publish authentication records, checked less than 24 hours before sending;
• automatic suppression of addresses that fail permanently;
• rate limits: 100 API requests per minute per project and environment, and an hourly sending limit per project at the mail server;
• holding messages at the mail server before delivery, for example when a project exceeds its limit;
• human review of reports and of unusual activity by us.

Apart from automatic suppression, the automatic hold of messages whose sender domain has no current DNS verification, and rate and sending limits, we do not make moderation decisions automatically.

The customer can complain about a decision by replying to our notice or by writing to mail@michael-ketzer.com. We review the complaint and tell the customer the outcome. Abuse is reported to mail@michael-ketzer.com.

[For legal review: DSA classification (mere conduit and/or hosting) and which of Articles 16 to 18 apply]

We may change the service where the change is reasonable for the customer, taking our interests into account, in particular to improve it, to follow technical developments, or for security or legal reasons.

We announce breaking changes to the API and the removal of features in text form at least 6 weeks in advance, unless a shorter period is required for security reasons or by law.

If a change materially affects the customer adversely, the customer may terminate the contract with effect from the date the change takes effect.

[For legal review: § 308 Nr. 4 BGB applies indirectly through § 307 BGB]

We may change these terms for the future for a valid reason, in particular a change in the law or in case law, a change to the service, or to close a gap in these terms. We send the changed wording in text form at least 6 weeks before it takes effect.

The customer may object to the change or terminate the contract before the change takes effect. If the customer does neither, the changed terms apply from that date. Our announcement points out the right to object, the period and this consequence of silence.

Changes to the main obligations, in particular the scope of the service, the fees (§ 7) and liability, need the customer’s express agreement.

[For legal review: how far deemed consent to changed terms is valid between businesses after BGH XI ZR 26/20]

We are liable without limitation for intent and gross negligence; for injury to life, body or health; under the Product Liability Act (Produkthaftungsgesetz); under an express guarantee we have given; and where we have fraudulently concealed a defect.

For slight negligence, we are liable only for breach of a core obligation. A core obligation is an obligation whose fulfilment makes the proper performance of the contract possible in the first place and on whose fulfilment the customer regularly relies. Our liability is then limited to damage that was foreseeable and typical for this kind of contract when the contract was made.

No-fault liability for defects that already exist when the contract is made (§ 536a(1), first alternative, BGB) is excluded.

For lost data, we are liable only for the effort that would have been typical to restore it if the customer had backed it up regularly and appropriately to the risk, using the means the service provides. [For legal review: the service has no complete export yet (§ 14); check whether this limit holds until it does]

These limitations also protect our employees, representatives and agents.

If the service is provided free of charge, we are liable only for intent and gross negligence. Paragraph (1) remains unaffected. [For legal review: liability wording for a free service (loan, § 599 BGB) versus a paid one (rental, BGH XII ZR 120/04)]

None of the limitations in this clause applies in the cases of paragraph (1).

[To verify: whether the act implementing Directive (EU) 2024/2853 (BT-Drs. 21/4297) has passed; it brings software into the Product Liability Act from 9 December 2026. Also BGH VIII ZR 121/04 on the definition of core obligations]

The contract runs for an indefinite period.

Either party may terminate it with a notice period of 30 days, in text form.

The right of either party to terminate for cause (§ 314 and § 543 BGB) is not affected.

Notice of termination must be given in text form.

When the contract ends, § 14 applies to switching and data export. We then delete customer data as described in the data processing agreement.

[For legal review: whether Letterpier is a “data processing service” under the Data Act (likely yes), and whether any relief under Article 31 applies during the preview. Check the Digital Omnibus changes before external launch]

The customer may switch to another provider or to its own infrastructure. It tells us so in text form; the switching notice period is at most two months and applies even if the notice period in § 13 is longer. [For legal review: check the ordinary notice period against this maximum]

A transition period of 30 days follows, during which the service continues and we support the switch. If this is technically impossible, we tell the customer within 14 working days, give our reasons and set an alternative transition period of at most seven months.

During the switch, we provide reasonable assistance, act with due care to maintain business continuity, inform the customer of known risks to continuity, and maintain a high level of security.

The customer can export:

• messages and their metadata, bodies and attachments;
• the original .eml files of received mail;
• events;
• domains and their DNS data;
• suppression lists;
• webhook configuration;
• audit logs.

Formats and timeline: messages, received mail and attachments through the API (JSON, and the original .eml for received mail) at any time during the retention period; on request, a JSON export of the project's configuration within 30 days.

After the transition period, the customer can retrieve its data for at least 30 days. We then delete it.

The contract ends when the switch has been completed successfully, and we confirm this to the customer in text form. If the customer does not want to switch but only to have its data erased, the contract ends at the end of the switching notice period.

From 12 January 2027, we charge nothing for switching. Until then, we charge at most our direct costs of the switch.

This clause and the documentation are our information on switching procedures and data formats under Article 26 of the Data Act.

Each party keeps confidential the information of the other party that is marked as confidential or is recognisably confidential, and uses it only for this contract.

This does not apply to information that is public, that the receiving party already knew, that it lawfully received from a third party, or that it must disclose by law or by order of an authority or court.

This obligation continues for three years after the contract ends. [For legal review: the period is a proposal]

For personal data, the data processing agreement takes precedence.

For the term of the contract, we grant the customer the non-exclusive, non-transferable right to use the service for its own business purposes, as described in these terms.

The customer keeps all rights to its content. It grants us the rights we need to provide the service, in particular to store, transmit and process that content.

We may use suggestions and feedback from the customer free of charge. This does not cover the customer’s confidential information or personal data.

Letterpier uses open-source software. Its licences, listed under open-source licences, take precedence for those components.

Resend is a trademark of Resend, Inc. Svix is a trademark of its owner. Letterpier is independent and is not affiliated with or endorsed by either. “Resend-compatible” describes compatibility with the tested SDK version for the endpoints listed in the compatibility table only.

German law applies, excluding the United Nations Convention on Contracts for the International Sale of Goods (CISG).

If the customer is a merchant (Kaufmann), a legal entity under public law or a special fund under public law, or has no general place of jurisdiction in Germany, the exclusive place of jurisdiction for all disputes arising from or in connection with this contract is Monheim am Rhein, Germany. For customers established in another Member State of the European Union, this is an agreement under Article 25 of Regulation (EU) No 1215/2012 (Brussels Ia).

We may also sue the customer at its general place of jurisdiction.

[For legal review: whether the clause works if the operator is not a Kaufmann (§ 38 ZPO). Operator status: not a Kaufmann. Also the form requirement of § 38(2) ZPO for customers without a general place of jurisdiction in Germany, whether acceptance in text form meets it, and whether to confirm the clause in the acceptance email (Article 25(2) Brussels Ia: durable record)]

Notices under this contract are given in text form, for example by email, unless these terms say otherwise. We send them to the email address the customer has given us.

Individually agreed terms take precedence over these terms (§ 305b BGB).

If a provision of these terms is or becomes invalid, the other provisions remain in effect. The statutory provisions apply in place of the invalid one (§ 306 BGB).

These terms are written in English. If we provide a translation, the English version governs.