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Hoot is built on top of the Nostr protocol, a simple and open protocol for decentralized communication. Instead of relying on traditional email servers, Hoot uses Nostr’s event-based architecture to send and receive messages.

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What is Nostr?

Nostr (Notes and Other Stuff Transmitted by Relays) is a decentralized protocol that enables censorship-resistant communication. At its core, Nostr consists of:
  • Events: Signed JSON objects that contain messages and data
  • Relays: WebSocket servers that store and forward events
  • Keys: Public/private keypairs for identity and encryption
Unlike traditional email, there’s no central authority. Users connect to multiple relays, and messages are distributed across the network.

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Nostr events

All data in Nostr is transmitted as events. Each event has:
  • Kind: A number indicating the event type
  • Content: The message or data payload
  • Tags: Metadata like recipients, parent messages, and subjects
  • Signature: Cryptographic proof of authenticity
// From src/mail_event.rs
pub const MAIL_EVENT_KIND: u16 = 2024;
Common event kinds in the Nostr ecosystem include:
  • Kind 0: Profile metadata (name, avatar, bio)
  • Kind 1: Short text notes
  • Kind 1059: Gift-wrapped encrypted events
  • Kind 2024: Hoot mail messages (custom)

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Custom kind 2024 for mail

Hoot uses a custom event kind (2024) specifically designed for email-like messages. These events include:
  • To/CC/BCC recipients: Specified using p tags
  • Subject: Stored in a subject tag
  • Threading: Parent event IDs for conversation threads
  • NIP-05 identifiers: Optional sender verification
// From src/mail_event.rs:23-69
pub struct MailMessage {
    pub to: Vec<PublicKey>,
    pub cc: Vec<PublicKey>,
    pub bcc: Vec<PublicKey>,
    pub parent_events: Option<Vec<EventId>>,
    pub subject: String,
    pub content: String,
    pub sender_nip05: Option<String>,
}
Kind 2024 events are never sent in plain text. They are always wrapped using NIP-59 gift wrapping before being sent to relays.

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How mail events are structured

When composing a message, Hoot creates a kind 2024 event with:
  1. P tags: One for each recipient in the To field
  2. P tags with “cc” marker: For CC recipients
  3. E tags: References to parent events for threading
  4. Subject tag: The email subject line
  5. Content: The message body
From src/mail_event.rs:28-38: 
for pubkey in &self.to {
    tags.push(Tag::public_key(*pubkey));
}

for pubkey in &self.cc {
    tags.push(Tag::custom(
        TagKind::p(),
        vec![pubkey.to_hex().as_str(), "cc"],
    ));
}

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Event verification

Every event received from relays is cryptographically verified before processing. From src/event_processing.rs:295-298: 
if event.verify().is_err() {
    error!("Event verification failed for event: {}", event.id);
    return;
}
This ensures that:
  • The event was signed by the claimed public key
  • The content hasn’t been tampered with
  • The event ID correctly represents the event data
Event verification happens automatically for all incoming messages. Invalid events are rejected and never stored in the database.

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Profile metadata events

Hoot uses standard Nostr kind 0 events for contact profiles. These events contain:
  • Display name
  • Avatar image URL
  • Bio/about text
  • NIP-05 identifier (for verification)
Profile metadata is cached locally and updated whenever newer metadata events are received from relays.