Rust

Cargo.toml

[dependencies]
reqwest = { version = "0.12", features = ["json"] }
serde_json = "1"
tokio = { version = "1", features = ["full"] }

src/main.rs

use serde_json::{json, Value};
use std::env;

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let key = env::var("SPACEPOST_API_KEY")?;

    let res = reqwest::Client::new()
        .post("https://api.spacepost.dev/emails")
        .bearer_auth(key)
        .header("Idempotency-Key", "welcome-user-42")
        .json(&json!({
            "from": "Acme <hello@acme.com>",
            "to": ["delivered@test.spacepost.dev"],
            "subject": "Hello from Rust",
            "html": "<p>It works.</p>"
        }))
        .send()
        .await?;

    let status = res.status();
    let body: Value = res.json().await?;
    if !status.is_success() {
        // { "statusCode": 422, "name": "validation_error", "message": "..." }
        return Err(format!("{}: {}", body["name"], body["message"]).into());
    }
    println!("sent {}", body["id"]);
    Ok(())
}