Herkos terms of use

Last updated: 20 September 2026. Canonical URL: https://herkos.app/terms

Herkos is a free, open-source mail client for the Nostr network, published by the Herkos project ("we", "the project"). These terms explain what you can expect from Herkos, what we expect from you, and the limits of both. They are short on purpose. If something here is unclear, write to hello@herkos.email.

The short version

• Herkos is software, not a service. We run no servers, hold no accounts and store nothing for you. You install a program; you do not sign up for anything.
• The software is licensed under the MIT licence. These terms do not take away any right that licence gives you.
• Your key is your account. Nobody — including us — can reset it, recover it or give you access if you lose it.
• Everything that travels beyond your device goes through independent operators (relays, Blossom servers, bridges). Their rules are theirs, not ours.
• The software comes with no warranty. It is young, it is being written in the open, and you use it at your own risk.

1. What Herkos is, and what it is not

Herkos is a client: a program that runs on your device and speaks the Nostr and Blossom protocols. It is a fork of Nostr Mail Client by nogringo, also MIT licensed.

The project does not operate a mail service. It does not create accounts, does not host mailboxes, does not deliver messages and does not keep copies of anything. When the app sends or receives mail, it talks to relays, Blossom servers and bridges chosen in Settings → Network and servers — services run by other people, under their own terms.

This matters for everything below: we cannot suspend your access, restore your data or intervene in a dispute with another user, because there is no account and no server to act on.

2. Accepting these terms

Installing or using Herkos means you accept these terms. If you do not accept them, do not install or use the app. You must also be old enough to agree to them where you live; Herkos is not intended for anyone under 16.

3. Licence, source code and forks

The Herkos source code is published under the MIT licence. You may use, copy, modify and redistribute it under that licence, including commercially. Nothing in this document restricts those rights; where this document and the MIT licence disagree about the code, the licence wins.

The name "Herkos" and the Herkos logo are not covered by the MIT licence. You may say that your program is based on or forked from Herkos, but do not publish a modified build under the Herkos name or logo, and do not present it as the official app. This is the ordinary rule for open-source projects: the code is free, the identity is not, because users rely on it to know what they are installing.

4. Your key is your responsibility

Herkos has no password and no account recovery. Your Nostr secret key (nsec), or the remote signer that holds it, is your identity and your mailbox.

• If you lose your key, your mail, your contacts and your identity are lost. No one can restore them.
• If someone else obtains your key, they become you: they can read your mail and write as you. Changing it is not possible; you can only create a new identity.
• Keeping a backup of the key is your job. The app helps you export it; where you then keep it is your decision and your risk.

We say this plainly because it is the single most important difference between Herkos and a conventional mail provider, and the one that surprises people.

5. Third-party services

Herkos connects to services the project does not run and cannot vouch for: Nostr relays, Blossom servers, SMTP bridges, NIP-05 domains, remote signers, scheduling DVMs and — if you enable notifications — a push server. The privacy policy lists each of them and what it can see.

Each of those operators sets its own terms, availability and data practices. They may refuse you, rate-limit you, delete data or disappear. The project is not responsible for what they do, does not promise that any of them will work, and does not act as an intermediary between you and them. You can change or remove every one of them in the app's settings.

The same applies to the store or platform you install Herkos from: its own terms govern that download.

6. The Herkos bridge

Mail between Nostr users never touches a mail server. Mail to or from a traditional address (Gmail, Outlook…) must pass through a bridge, which by definition can read it.

If and when the project operates its own bridge for @herkos.email senders, these rules apply to it:

• It serves the project's own addresses only. Herkos does not hand out @herkos.email addresses to the public and is not a mail provider.
• It is provided as is, with sending limits, no delivery guarantee and no support commitment. Message delivery to third-party providers depends on their spam filtering, not on us.
• It may be paused, restricted or shut down at any time, without notice, in particular if it is abused.

Bridges operated by other people are third-party services under section 5.

7. Acceptable use

You are responsible for what you send and publish with Herkos. Do not use it to:

• send unsolicited bulk mail, or anything a reasonable person would call spam;
• impersonate another person, project or organisation, including this one;
• distribute malware, phishing, or material that is illegal where you or your recipient are;
• harass, threaten or endanger anyone;
• attack, overload or circumvent the limits of relays, bridges or any other service the app connects to.

We cannot enforce this — there is no account to close. Relay and bridge operators can and will: they may block your key or your address. And the law applies to you regardless of what protocol you used.

8. No warranty

Herkos is provided "as is", without warranty of any kind, express or implied, including but not limited to warranties of merchantability, fitness for a particular purpose and non-infringement. This is the MIT licence's disclaimer, and it is not decoration: the software is in early development, the protocols it uses are evolving, and bugs that lose or expose mail are possible.

In particular, we do not promise that the app will run without errors, that mail will arrive, that it will arrive on time, that anything you store will survive an update, or that any relay, bridge or server will be reachable.

Do not use Herkos as the only channel for anything you cannot afford to lose or have delayed, and do not use it where lives, safety or legal deadlines depend on a message arriving. If you are in a situation where being identified would put you in danger, read the security page first: it says what Herkos protects and, just as important, what it does not.

9. Limitation of liability

To the fullest extent permitted by law, the project and its contributors are not liable for any indirect, incidental, special or consequential damages, nor for loss of data, loss of access to an identity, loss of profits or loss of opportunity, arising from the use of or inability to use Herkos — even if we were told such damage was possible.

Nothing here excludes liability that cannot be excluded by law, and if you use Herkos as a consumer in the European Union, your mandatory consumer rights are unaffected by this document.

10. Changes to the app and to these terms

Herkos is developed in the open and changes often. Features may be added, altered or removed, and a release may require you to migrate data. There is no service level, no support obligation and no guarantee that any version will keep working.

We will update these terms when the app's behaviour makes it necessary, and record the date at the top. The source of truth is TERMS.md in the repository; the published page is a copy of it. Material changes will be noted in the release notes. Continuing to use the app after a change means accepting the new version; if you do not, stop using it — there is no subscription to cancel.

11. Law and disputes

These terms are governed by Spanish law, without prejudice to the mandatory rules of the country where you live if you are a consumer. Before going to court, please write to hello@herkos.email: almost everything is a misunderstanding that a message fixes.

12. Contact

hello@herkos.email · https://herkos.app · privacy policy · security