ENCRYPTED BY DESIGN

Security architecture

USOM Mail stores received mail encrypted at rest and splits the key so no single place holds the whole of it. We are honest about what that protects — and where it does not reach yet.

How it is protected

  • AES-256-GCM

    Encrypted at restBody, subject and sender are encrypted with a per-address key before being stored. Nothing is left as plain text in the database.

  • 2 OF 4 SHARES

    The assembled key is not storedThe encryption key is split into four shares with Shamir secret sharing; two are used to reconstruct it. The assembled key itself is stored nowhere.

  • RECEIVING ONLY

    No sending surfaceUSOM Mail is focused on receiving and reading. Because there is no arbitrary-send endpoint, it cannot be used as a relay for spoofed mail.

  • IDENTITY SPLIT

    Authentication is separate from the inboxYou can use it without signing in. Even when you link a Google account, all that is stored is the provider and the ID on that provider — never the bare email address.

From arrival to reading

Received mail is stored encrypted with a per-address key. Here is the flow up to when a person reads it in a browser, or an AI agent reads it over MCP.

How mail is received and encryptedUSOM Mail receives a verification email from an external service, stores it encrypted, and then a person or an AI agent reads it.AmazonNetflixGitHubOTHEROTHERUSOMMultiple receiving-only addressesconfirm@usom.exampleagent@usom.example+ moreStored encryptedPeopleRead in a browserAI agentsFetch over MCP
  1. When mail arrives, its body, subject and sender are encrypted with a key dedicated to that address and stored.
  2. The key is split into four shares and managed separately; the assembled key is not stored.
  3. Only when you open the inbox is the key reassembled from two shares to decrypt.
  4. Mail past its retention period is deleted along with the ciphertext.

Retention and deletion

Received-mail retention depends on your plan (30 days on the free plan). For details, see Plans; for how to delete, see the Guide. Account deletion has a 30-day grace period, and signing in again with the same account within that period cancels it.

AI agent authentication

Agents connect with a Bearer Token. When a wallet signature is used, the signature is only for identity verification and does not authorize payment. You do not need to send a private key or seed phrase to USOM. Do not leave the token in URLs, logs or public files. The connection spec is in Agent Identity Mailbox.

Current limits

  • Key shares are currently managed by role within the same database, not fully physically separated (the design does make separation easy).
  • On a shared PC or someone else's device, the inbox may be visible from a session left in the browser. Sign out when you are done.
  • As with temporary email in general, a sending service may reject disposable addresses, or delivery may be delayed so mail does not arrive.
  • To the minimum extent required for legal or abuse response, operators may inspect stored data (see Terms, sections 7 and 8).
  • Inbound sender addresses are not yet cryptographically verified (no DMARC enforcement), so a message's "From" can be spoofed like ordinary email — treat it with the same caution as any other inbox.
  • Automatic spam classification is currently paused while we rework it. Mail still arrives; it just is not pre-sorted for now.
  • Addresses created in the iOS app keep their key only on that device (and any device synced to the same Apple ID via iCloud Keychain), not on our servers. Mail to those addresses cannot be read from the web app or other devices unless you opt back into server-held keys from iOS Settings.

Reporting a vulnerability

If you notice a problem in the design or implementation, please contact us via Contact. Send detailed reproduction steps or exploit code to us directly, not in public.

This design keeps changing. We announce major changes on this page and in the FAQ.