wasix-sendmail

A sendmail-compatible email sender with multiple backends.

Features

• Supports all common sendmail flags
• Multiple backends: SMTP relay, REST API, and file output

Building for WASIX

Build the WASM module:

cargo build --release --target=wasm32-wasmer-wasi

This compiles the project to target/wasm32-wasmer-wasi/release/sendmail.wasm. You can then run that binary either directly or via the supplied wasmer.toml (wasmer run .)

Usage

Read email from stdin and send:

echo "Subject: Test\n\nBody" | sendmail recipient@example.com

Read recipients from email headers:

echo "To: user@example.com\nSubject: Test\n\nBody" | sendmail -t

Set envelope sender:

echo "Subject: Test\n\nBody" | sendmail -f sender@example.com recipient@example.com

Configuration

The backend is selected automatically based on which environment variables are set.

1. File Backend (highest priority)

For debugging and testing:

• SENDMAIL_FILE_PATH - Path to output file where emails will be written

2. SMTP Relay Backend (second highest priority)

For sending via an SMTP relay:

• SENDMAIL_RELAY_HOST - SMTP relay hostname (required)
• SENDMAIL_RELAY_PORT - SMTP relay port (default: 587)
• SENDMAIL_RELAY_PROTO - Protocol (e.g., tls, starttls, plain, opportunistic) (default: opportunistic)
• SENDMAIL_RELAY_USER - Username for authentication (optional)
• SENDMAIL_RELAY_PASS - Password for authentication (optional)

If a username or password is specified, you also need to specify the other one.

3. REST API Backend (lowest priority)

For sending via a custom REST API:

• SENDMAIL_API_URL - URL of the mail endpoint (required)
• SENDMAIL_API_SENDER - Default sender address (required)
• SENDMAIL_API_TOKEN - Authentication token (required)

Note: When deploying to wasmer edge the environment variables for the REST API will be automatically populated.

Note: If no backend is configured, sendmail will exit with an error.

All three API variables must be set for the REST API backend to be used.