Lettermint

Rust client library for the Lettermint email service. HTTP client-agnostic — ships with a reqwest implementation, or bring your own by implementing the Client trait.

Usage

[dependencies]
lettermint = { version = "0.1", features = ["reqwest-rustls"] }
tokio = { version = "1", features = ["rt", "macros"] }

Send an email

use lettermint::api::email::SendEmailRequest;
use lettermint::reqwest::LettermintClient;
use lettermint::Query;

#[tokio::main]
async fn main() {
    let client = LettermintClient::new("your-api-token");

    let req = SendEmailRequest::builder()
        .from("sender@yourdomain.com")
        .to(vec!["recipient@example.com".into()])
        .subject("Hello from Lettermint")
        .text("Plain text body")
        .build();

    let resp = req.execute(&client).await.unwrap();
    println!("Sent: {} ({})", resp.message_id, resp.status);
}

HTML + text with all options

use lettermint::api::email::{SendEmailRequest, Attachment};
use lettermint::reqwest::LettermintClient;
use lettermint::Query;
use std::collections::HashMap;

async fn send_full(client: &LettermintClient) {
    let req = SendEmailRequest::builder()
        .from("Jane <jane@yourdomain.com>")
        .to(vec!["user@example.com".into()])
        .subject("Monthly update")
        .html("<h1>Update</h1><p>Here's what happened.</p>")
        .text("Here's what happened.")
        .cc(vec!["team@example.com".into()])
        .bcc(vec!["archive@example.com".into()])
        .reply_to(vec!["support@yourdomain.com".into()])
        .headers(HashMap::from([
            ("X-Campaign".into(), "monthly-update".into()),
        ]))
        .attachments(vec![
            Attachment::new("report.pdf", "<base64-encoded-content>"),
            Attachment::inline("logo.png", "<base64-encoded-logo>", "logo"),
        ])
        .metadata(HashMap::from([
            ("campaign_id".into(), "2025-03".into()),
        ]))
        .tag("newsletter")
        .route("my-route")
        .idempotency_key("monthly-update-2025-03")
        .build();

    let resp = req.execute(client).await.unwrap();
    println!("{:?}", resp);
}

Batch sending

Send up to 500 emails in a single request:

use lettermint::api::email::{SendEmailRequest, BatchSendRequest};
use lettermint::reqwest::LettermintClient;
use lettermint::Query;

async fn send_batch(client: &LettermintClient) {
    let batch = BatchSendRequest::new(vec![
        SendEmailRequest::builder()
            .from("sender@yourdomain.com")
            .to(vec!["alice@example.com".into()])
            .subject("Hello Alice")
            .text("Hi Alice!")
            .build(),
        SendEmailRequest::builder()
            .from("sender@yourdomain.com")
            .to(vec!["bob@example.com".into()])
            .subject("Hello Bob")
            .text("Hi Bob!")
            .build(),
    ])
    .expect("batch must be 1-500 emails");

    let responses = batch.execute(client).await.unwrap();
    for resp in responses {
        println!("Sent: {} ({})", resp.message_id, resp.status);
    }
}

Ping

Check API connectivity and validate credentials:

use lettermint::api::ping::PingRequest;
use lettermint::reqwest::LettermintClient;
use lettermint::Query;

async fn ping(client: &LettermintClient) {
    let resp = PingRequest.execute(client).await.unwrap();
    println!("API status: {}", resp.status);
}

Webhook verification

use lettermint::webhook::Webhook;

let wh = Webhook::new("whsec_your_webhook_secret");

// Simple verification — returns parsed JSON payload
let payload = wh.verify(raw_body, signature_header).unwrap();
println!("Verified event: {}", payload);

// Full header verification — returns WebhookEvent with metadata
let event = wh.verify_headers(
    signature_header,
    delivery_header,    // X-Lettermint-Delivery
    event_header,       // X-Lettermint-Event
    attempt_header,     // X-Lettermint-Attempt
    raw_body,
).unwrap();
println!("Event: {:?}, attempt: {:?}", event.event, event.attempt);

Error handling

use lettermint::{Query, QueryError};

match req.execute(&client).await {
    Ok(resp) => println!("Sent: {}", resp.message_id),
    Err(QueryError::Validation { errors, message, .. }) => {
        eprintln!("Validation failed: {message:?}, fields: {errors:?}");
    }
    Err(QueryError::Authentication { message, .. }) => {
        eprintln!("Auth failed: {message:?}");
    }
    Err(QueryError::RateLimit { message, .. }) => {
        eprintln!("Rate limited: {message:?}");
    }
    Err(e) => eprintln!("Error: {e}"),
}

Features

To use your own HTTP client, implement the Client trait and skip the reqwest features entirely.

Testing

Unit tests:

cargo test --all-features

Integration tests

Integration tests hit the live Lettermint API using test addresses that don't count toward quotas:

LETTERMINT_API_TOKEN=your-token \
LETTERMINT_SENDER=you@yourdomain.com \
cargo test --test integration --all-features -- --ignored

License

Dual-licensed under MIT or Apache 2.0.