# Missive
Compose, deliver, and test emails in Rust. Plug and play.
Missive comes with adapters for popular transactional email providers including Amazon SES, Mailgun, Resend, SendGrid, Postmark, SMTP, and more. Zero configuration required for most setups.
## Requirements
Rust 1.75+ (async traits)
## Quick Start
Add to your `.env`:
```bash
# ---- Missive Email ----
EMAIL_PROVIDER=resend
EMAIL_FROM=noreply@example.com
RESEND_API_KEY=re_xxxxx
```
Send emails:
```rust
use missive::{Email, deliver};
let email = Email::new()
.to("user@example.com")
.subject("Welcome!")
.text_body("Thanks for signing up.");
deliver(&email).await?;
```
That's it. No configuration code, no builder structs, no initialization.
## Installation
Add missive to your `Cargo.toml`:
```toml
[dependencies]
missive = { version = "0.1", features = ["resend"] }
```
Enable the feature for your email provider. See [Feature Flags](#feature-flags) for all options.
## Providers
Missive supports popular transactional email services out of the box:
| SMTP | `smtp` | `SMTP_HOST`, `SMTP_PORT`, `SMTP_USERNAME`, `SMTP_PASSWORD` |
| Resend | `resend` | `RESEND_API_KEY` |
| SendGrid | `sendgrid` | `SENDGRID_API_KEY` |
| Postmark | `postmark` | `POSTMARK_API_KEY` |
| Brevo | `brevo` | `BREVO_API_KEY` |
| Mailgun | `mailgun` | `MAILGUN_API_KEY`, `MAILGUN_DOMAIN` |
| Mailjet | `mailjet` | `MAILJET_API_KEY`, `MAILJET_SECRET_KEY` |
| Amazon SES | `amazon_ses` | `AWS_REGION`, `AWS_ACCESS_KEY_ID`, `AWS_SECRET_ACCESS_KEY` |
| Mailtrap | `mailtrap` | `MAILTRAP_API_KEY` |
| Unsent | `unsent` | `UNSENT_API_KEY` |
| Local | `local` | (none) |
| Logger | (always available) | (none) |
Configure which provider to use with the `EMAIL_PROVIDER` environment variable:
```bash
EMAIL_PROVIDER=sendgrid
```
## Feature Flags
Missive uses Cargo features for conditional compilation - only the providers you enable are compiled into your binary. This keeps binaries small and compile times fast.
### Minimal: Single Provider
If you only use one provider, enable just that feature:
```toml
[dependencies]
missive = { version = "0.1", features = ["resend"] }
```
```bash
RESEND_API_KEY=re_xxxxx
# EMAIL_PROVIDER is auto-detected when only one is enabled
```
This gives you the smallest binary and fastest compile. You'd need to recompile to switch providers.
### Flexible: Multiple Providers
For runtime flexibility (e.g., different providers per environment), enable multiple:
```toml
[dependencies]
missive = { version = "0.1", features = ["smtp", "resend", "local"] }
```
Then configure per environment in `.env`:
```bash
# ---- Missive Email ----
# Development: local mailbox preview at /dev/mailbox
EMAIL_PROVIDER=local
EMAIL_FROM=noreply@example.com
```
```bash
# ---- Missive Email ----
# Staging: test with Resend
EMAIL_PROVIDER=resend
EMAIL_FROM=noreply@example.com
RESEND_API_KEY=re_test_xxx
```
```bash
# ---- Missive Email ----
# Production: your own SMTP
EMAIL_PROVIDER=smtp
EMAIL_FROM=noreply@example.com
SMTP_HOST=mail.example.com
SMTP_USERNAME=apikey
SMTP_PASSWORD=your-api-key
```
Same compiled binary, different behavior per environment.
### Auto-Detection
When `EMAIL_PROVIDER` is not set, Missive automatically detects which provider to use based on:
1. **Available API keys** - checks for `RESEND_API_KEY`, `SENDGRID_API_KEY`, etc.
2. **Enabled features** - only considers providers whose feature is compiled in
3. **Fallback to local** - if the `local` feature is enabled and no API keys found
**Detection order:** Resend → SendGrid → Postmark → Unsent → SMTP → Local
This means zero-config for simple setups:
```toml
missive = { version = "0.1", features = ["resend"] }
```
```bash
RESEND_API_KEY=re_xxxxx
# No EMAIL_PROVIDER needed - Resend is auto-detected
```
Use `EMAIL_PROVIDER` explicitly when:
- Multiple providers are enabled and you want to choose one
- You want to override auto-detection
- You're using `logger` or `logger_full` (no API key to detect)
### Bundles
```toml
# Development setup (local + preview UI)
missive = { version = "0.1", features = ["dev"] }
# Everything (all providers + templates)
missive = { version = "0.1", features = ["full"] }
```
### Available Features
| `smtp` | SMTP provider via lettre |
| `resend` | Resend API |
| `sendgrid` | SendGrid API |
| `postmark` | Postmark API |
| `unsent` | Unsent API |
| `local` | LocalMailer - in-memory storage + test assertions |
| `preview` | Web UI for viewing local emails (Axum) |
| `preview-axum` | Preview UI with Axum |
| `preview-actix` | Preview UI with Actix |
| `templates` | Askama template integration |
| `metrics` | Prometheus-style metrics |
| `dev` | Enables `local` + `preview` |
| `full` | All providers + templates + preview |
## Environment Variables
### Global Settings
| `EMAIL_PROVIDER` | Which provider to use | `smtp` |
| `EMAIL_FROM` | Default sender email | (none) |
| `EMAIL_FROM_NAME` | Default sender name | (none) |
### Provider-Specific
**SMTP:**
| `SMTP_HOST` | SMTP server hostname | (required) |
| `SMTP_PORT` | SMTP server port | `587` |
| `SMTP_USERNAME` | SMTP username | (optional) |
| `SMTP_PASSWORD` | SMTP password | (optional) |
| `SMTP_TLS` | TLS mode: `required`, `opportunistic`, `none` | `required` |
**API Providers:**
| `RESEND_API_KEY` | Resend |
| `SENDGRID_API_KEY` | SendGrid |
| `POSTMARK_API_KEY` | Postmark |
| `UNSENT_API_KEY` | Unsent |
## Composing Emails
### Basic Email
```rust
use missive::Email;
let email = Email::new()
.from("sender@example.com")
.to("recipient@example.com")
.subject("Hello!")
.text_body("Plain text content")
.html_body("<h1>HTML content</h1>");
```
### With Display Names
```rust
let email = Email::new()
.from(("Alice Smith", "alice@example.com"))
.to(("Bob Jones", "bob@example.com"))
.subject("Meeting tomorrow");
```
### Multiple Recipients
```rust
let email = Email::new()
.to("one@example.com")
.to("two@example.com")
.cc("cc@example.com")
.bcc("bcc@example.com")
.reply_to("replies@example.com");
```
### Custom Headers
```rust
let email = Email::new()
.header("X-Custom-Header", "custom-value")
.header("X-Priority", "1");
```
### Provider-Specific Options
Pass options specific to your email provider:
```rust
// Resend: tags and scheduling
let email = Email::new()
.provider_option("tags", json!([{"name": "category", "value": "welcome"}]))
.provider_option("scheduled_at", "2024-12-01T00:00:00Z");
// SendGrid: categories and tracking
let email = Email::new()
.provider_option("categories", json!(["transactional", "welcome"]))
.provider_option("tracking_settings", json!({"click_tracking": {"enable": true}}));
```
## Custom Recipient Types
Implement `ToAddress` for your types to use them directly in email builders:
```rust
use missive::{Address, ToAddress, Email};
struct User {
name: String,
email: String,
}
impl ToAddress for User {
fn to_address(&self) -> Address {
Address::with_name(&self.name, &self.email)
}
}
// Now use directly:
let user = User { name: "Alice".into(), email: "alice@example.com".into() };
let email = Email::new()
.to(&user)
.subject("Welcome!");
```
## Email Validation
Missive provides email address validation:
```rust
use missive::Address;
// Lenient (logs warnings for suspicious input)
let addr = Address::new("user@example.com");
// Strict RFC 5321/5322 validation
let addr = Address::parse("user@example.com")?;
let addr = Address::parse_with_name("Alice", "alice@example.com")?;
// International domain names (IDN/Punycode)
let addr = Address::new("user@example.jp");
let ascii = addr.to_ascii()?; // Converts to punycode if needed
```
## Attachments
### From Bytes
```rust
use missive::{Email, Attachment};
let email = Email::new()
.to("user@example.com")
.subject("Your report")
.attachment(
Attachment::from_bytes("report.pdf", pdf_bytes)
.content_type("application/pdf")
);
```
### From File
```rust
// Eager loading (reads file immediately)
let attachment = Attachment::from_path("/path/to/file.pdf")?;
// Lazy loading (reads file at send time)
let attachment = Attachment::from_path_lazy("/path/to/large-file.zip")?;
```
### Inline Attachments (HTML Embedding)
```rust
let email = Email::new()
.html_body(r#"<img src="cid:logo">"#)
.attachment(
Attachment::from_bytes("logo.png", png_bytes)
.inline()
.content_id("logo")
);
```
## Testing
Use `LocalMailer` to capture emails in tests:
```rust
use missive::{Email, deliver_with, configure};
use missive::providers::LocalMailer;
use missive::testing::*;
#[tokio::test]
async fn test_welcome_email() {
let mailer = LocalMailer::new();
configure(mailer.clone());
// Your code that sends an email
send_welcome_email("user@example.com").await;
// Assertions
assert_email_sent(&mailer);
assert_email_to(&mailer, "user@example.com");
assert_email_subject_contains(&mailer, "Welcome");
assert_email_count(&mailer, 1);
}
```
### Available Assertions
| `assert_email_sent(&mailer)` | At least one email was sent |
| `assert_no_emails_sent(&mailer)` | No emails were sent |
| `assert_email_count(&mailer, n)` | Exactly n emails were sent |
| `assert_email_to(&mailer, email)` | Email was sent to address |
| `assert_email_from(&mailer, email)` | Email was sent from address |
| `assert_email_subject(&mailer, subject)` | Email has exact subject |
| `assert_email_subject_contains(&mailer, text)` | Subject contains text |
| `assert_email_html_contains(&mailer, text)` | HTML body contains text |
| `assert_email_text_contains(&mailer, text)` | Text body contains text |
| `refute_email_to(&mailer, email)` | No email was sent to address |
### Simulating Failures
```rust
let mailer = LocalMailer::new();
mailer.set_failure("SMTP connection refused");
let result = deliver_with(&email, &mailer).await;
assert!(result.is_err());
```
### Flush Emails
```rust
// Get and clear all emails atomically
let emails = flush_emails(&mailer);
assert_eq!(emails.len(), 3);
// Mailer is now empty
assert_no_emails_sent(&mailer);
```
## Mailbox Preview
View sent emails in your browser during development:
```rust
use missive::providers::LocalMailer;
use missive::preview::mailbox_router;
// Create mailer and get shared storage
let mailer = LocalMailer::new();
let storage = mailer.storage();
// Configure as global mailer
missive::configure(mailer);
// Mount the preview UI in your Axum router
let app = Router::new()
.nest("/mailbox", mailbox_router(storage))
.route("/", get(home));
```
Then visit `http://localhost:3000/mailbox` to see sent emails.
### Features
- View all sent emails
- HTML and plain text preview
- View email headers
- Download attachments
- Delete individual emails or clear all
- JSON API for programmatic access
## Per-Call Mailer Override
Override the global mailer for specific emails:
```rust
use missive::{Email, deliver_with};
use missive::providers::ResendMailer;
// Use a different API key for this one email
let special_mailer = ResendMailer::new("different_api_key");
let email = Email::new()
.to("vip@example.com")
.subject("Special delivery");
deliver_with(&email, &special_mailer).await?;
```
## Async Emails
Missive's `deliver()` is already async. For fire-and-forget sending:
```rust
// Using tokio::spawn
tokio::spawn(async move {
if let Err(e) = deliver(&email).await {
tracing::error!("Failed to send email: {}", e);
}
});
```
For reliable delivery, use a job queue like [apalis](https://github.com/geofmureithi/apalis):
```rust
use apalis::prelude::*;
#[derive(Debug, Serialize, Deserialize)]
struct SendEmailJob {
to: String,
subject: String,
body: String,
}
async fn send_email(job: SendEmailJob, _ctx: JobContext) -> Result<(), Error> {
let email = Email::new()
.to(&job.to)
.subject(&job.subject)
.text_body(&job.body);
deliver(&email).await?;
Ok(())
}
```
## Metrics
Enable Prometheus-style metrics with `features = ["metrics"]`:
```toml
missive = { version = "0.1", features = ["resend", "metrics"] }
```
Missive emits these metrics:
| `missive_emails_total` | Counter | provider, status | Total emails sent |
| `missive_delivery_duration_seconds` | Histogram | provider | Delivery duration |
| `missive_batch_total` | Counter | provider, status | Batch operations |
| `missive_batch_size` | Histogram | provider | Emails per batch |
Install a recorder in your app to collect them:
```rust
// Using metrics-exporter-prometheus
metrics_exporter_prometheus::PrometheusBuilder::new()
.install()
.expect("failed to install Prometheus recorder");
```
If you don't install a recorder, metric calls are no-ops (zero overhead).
## Observability
Missive uses the `tracing` crate for observability. All email deliveries create spans:
```
missive.deliver { provider="resend", to=["user@example.com"], subject="Hello" }
```
Configure with any tracing subscriber:
```rust
tracing_subscriber::fmt::init();
```
## Error Handling
All errors are returned as `MailError`:
```rust
use missive::{deliver, MailError};
match deliver(&email).await {
Ok(result) => println!("Sent with ID: {}", result.message_id),
Err(MailError::MissingField(field)) => println!("Missing: {}", field),
Err(MailError::InvalidAddress(msg)) => println!("Bad address: {}", msg),
Err(MailError::ProviderError { provider, message, .. }) => {
println!("{} error: {}", provider, message);
}
Err(e) => println!("Error: {}", e),
}
```
## Logger Provider
Use `EMAIL_PROVIDER=logger` to only log emails without sending:
```bash
# Brief logging (just recipients and subject)
EMAIL_PROVIDER=logger
# Full logging (all fields, bodies at debug level)
EMAIL_PROVIDER=logger_full
```
Useful for staging environments or debugging.
## Templates
Enable `features = ["templates"]` for Askama integration:
```rust
use missive::{Email, EmailTemplate};
use askama::Template;
#[derive(Template)]
#[template(path = "welcome.html")]
struct WelcomeEmail {
username: String,
action_url: String,
}
let template = WelcomeEmail {
username: "Alice".into(),
action_url: "https://example.com/verify".into(),
};
let email = Email::new()
.to("alice@example.com")
.subject("Welcome!")
.render_html(&template)?;
```
## API Reference
### Core Functions
| `deliver(&email)` | Send email using global mailer |
| `deliver_with(&email, &mailer)` | Send email using specific mailer |
| `deliver_many(&emails)` | Send multiple emails |
| `configure(mailer)` | Set the global mailer |
| `init()` | Initialize from environment variables |
| `is_configured()` | Check if email is properly configured |
### Email Builder
| `.from(addr)` | Set sender |
| `.to(addr)` | Add recipient |
| `.cc(addr)` | Add CC recipient |
| `.bcc(addr)` | Add BCC recipient |
| `.reply_to(addr)` | Add reply-to address |
| `.subject(text)` | Set subject line |
| `.text_body(text)` | Set plain text body |
| `.html_body(html)` | Set HTML body |
| `.attachment(att)` | Add attachment |
| `.header(name, value)` | Add custom header |
| `.provider_option(key, value)` | Set provider-specific option |
| `.assign(key, value)` | Set template variable |
## Documentation
For more detailed guides, see the [docs/](./docs/) folder:
- [Providers](./docs/providers.md) - Detailed configuration for each email provider
- [Testing](./docs/testing.md) - Complete testing guide with all assertion functions
- [Observability](./docs/observability.md) - Telemetry, metrics, Grafana dashboards, and alerting
- [Preview](./docs/preview.md) - Mailbox preview UI configuration
- [Templates](./docs/templates.md) - Askama template integration
## Acknowledgments
Missive's design is inspired by [Swoosh](https://github.com/swoosh/swoosh), the excellent Elixir email library.
## License
MIT