3. Get your chat ID (use [@getidsbot](https://t.me/getidsbot) or debug mode in Telegram client).

### Example configuration
```toml
api_key = "replace-with-your-telegram-bot-token"
api_gateway = "https://api.telegram.org"
listen_on = "127.0.0.1:1025"
unknown = "relay"
fields = ["date", "from", "subject"]
domains = ["example.com", "localhost"]

default = 0

[recipients]
"admin@example.com" = 12345678
"alerts@example.com" = -10012345678
```

To catch bounces (so they wouldn't stuck in upper mail server) make sure sender
envelope address is real as required by mail library (actually not sure whether
this applies to mailin). For example Postfix has to be tweaked like this:

$config_directory/main.cf:
	smtp_generic_maps = hash:$config_directory/generic

$config_directory/generic:
	""	postmaster@example.com
	<>	postmaster@example.com

Actually not sure which one works...

---

## Usage

### Run
```bash
./smtp2tg -c /path/to/smtp2tg.toml

		}
	}
	let settings: config::Config = config::Config::builder()
		.set_default("api_gateway", "https://api.telegram.org").stack()?
		.set_default("fields", vec!["date", "from", "subject"]).stack()?
		.set_default("hostname", "smtp.2.tg").stack()?
		.set_default("listen_on", "0.0.0.0:1025").stack()?
		.set_default("unknown", "relay").stack()?
		.set_default("domains", vec!["localhost",
			hostname::get().expect("Failed to get current hostname")
			.to_str().expect("Can't convert hostname to string, bad UTF-8?")]).stack()?
		.add_source(config::File::from(config_file))
		.build()
		.with_context(|| format!("[{config_file:?}] there was an error reading config\n\
			\tplease consult \"smtp2tg.toml.example\" for details"))?;

		INVALID_CREDENTIALS,
		NO_MAILBOX,
		OK
	},
};
use regex::{
	Regex,
	RegexBuilder,
	escape,
};
use stacked_errors::{
	Result,
	StackableErr,
	bail,
};

}

/// `MailServer` Central object with TG api and configuration
#[derive(Clone, Debug)]
pub struct MailServer {
	data: Vec<u8>,
	headers: Option<SomeHeaders>,
	relay: bool,
	tg: Arc<TelegramTransport>,
	fields: HashSet<String>,
	address: Regex,
}

impl MailServer {
	/// Initializes the mail server: sets up the Telegram API client and

			.context("[smtp2tg.toml] missing \"api_key\" parameter.\n")?;
		let mut recipients = HashMap::new();
		for (name, value) in settings.get_table("recipients")
			.expect("[smtp2tg.toml] missing table \"recipients\".\n")
		{
			let value = value.into_int()
				.context("[smtp2tg.toml] \"recipient\" table values should be integers.\n")?;
			recipients.insert(name, value);
			recipients.insert(name.to_lowercase().replace('.', ""), value);
		}

		let tg = Arc::new(TelegramTransport::new(api_key, recipients, &settings)?);
		let fields = HashSet::<String>::from_iter(settings.get_array("fields")
			.expect("[smtp2tg.toml] \"fields\" should be an array")
			.iter().map(|x| x.clone().into_string().expect("should be strings")));
		let mut domains: HashSet<String> = HashSet::new();
		let extra_domains = settings.get_array("domains").stack()?;
		for domain in extra_domains {
			let domain = domain.to_string().to_lowercase();
			if RE_DOMAIN.is_match(&domain) {
				domains.insert(domain);
			} else {
				panic!("[smtp2tg.toml] can't check of domains in \"domains\": {domain}");
			}
		}
		let domains = domains.into_iter().map(|s| escape(&s))
			.collect::<Vec<String>>().join("|");
		let address = Regex::new(&format!("^[a-z0-9][-a-z0-9]*(@({domains}))?$")).stack()?;
		let address = RegexBuilder::new(&format!("^[a-z0-9][a-z0-9.-]*(@({domains}))?$"))
		let relay = match settings.get_string("unknown")
			.context("[smtp2tg.toml] can't get \"unknown\" policy.\n")?.as_str()
		{
			"relay" => true,
			.case_insensitive(true).build().stack()?;
			"deny" => false,
			_ => {
				bail!("[smtp2tg.toml] \"unknown\" should be either \"relay\" or \"deny\".\n");
			},
		};

		Ok(MailServer {
			data: vec!(),
			headers: None,
			relay,
			tg,
			fields,
			address,
		})
	}

	/// Retrieves the Telegram chat ID for a given email address, checks that

		if let Some(headers) = &self.headers {
			let mail = mail_parser::MessageParser::new().parse(&self.data)
				.context("Failed to parse mail.")?;

			// Adding all known addresses to recipient list, for anyone else adding default
			// Also if list is empty also adding default
			let mut rcpt: HashSet<&ChatPeerId> = HashSet::new();
			if headers.to.is_empty() && !self.relay {
			if headers.to.is_empty() {
				bail!("Relaying is disabled, and there's no destination address");
			}
			for item in &headers.to {
				rcpt.insert(self.get_id(item)?);
			};
			if rcpt.is_empty() {
				self.tg.debug("No recipient or envelope address.").await?;

	/// Just deny plain auth
	fn auth_plain (&mut self, _authorization_id: &str, _authentication_id: &str, _password: &str) -> Response {
		INVALID_CREDENTIALS
	}

	/// Verify whether address is deliverable
	fn rcpt (&mut self, to: &str) -> Response {
		if self.relay || self.get_id(to).is_ok() {
		if self.get_id(to).is_ok() {
			OK
		} else {
			NO_MAILBOX
		}
	}

	/// Save headers we need

	///
	/// # Returns
	/// * `Result<&ChatPeerId>` - Chat ID if found.
	///
	/// # Errors
	/// Returns an error if `name` is not configured.
	pub fn get (&self, name: &str) -> Result<&ChatPeerId> {
		self.recipients.get(name)
		self.recipients.get(&name.to_lowercase().replace('.', ""))
			.with_context(|| format!("Recipient \"{name}\" not found in configuration"))
	}

	/// Sends a text message to a specified chat.
	///
	/// # Arguments
	/// * `to` - Target chat ID.

/// network access is performed while constructing it.
fn build_server () -> Result<MailServer> {
	let settings = config::Config::builder()
		.add_source(config::File::from_str(r#"
			api_key = "test-api-key"
			api_gateway = "https://api.telegram.org"
			default = 0
			unknown = "relay"
			fields = ["date", "from", "subject"]
			domains = ["example.com"]

			[recipients]
			"someone@example.com" = 1
			"root" = -1
		"#, config::FileFormat::Toml))
		.build()
		.stack()?;
	MailServer::new(settings)
}

#[test]
fn get_id_returns_configured_recipient () -> Result<()> {
fn get_id_properly_resolves_addresses () -> Result<()> {
	let server = build_server()?;
	let cases = [
		("someone@example.com", 1),
		("someone", 0),
		("root", -1),
		("unknown@example.com", 0),
		("SOMEONE@example.com", 1),	// uppercase local part
		("someone@EXAMPLE.COM", 1),	// uppercase domain
		("some.one@example.com", 1),	// functionally equivalent to skipping '.'
		("some-one-2", 0),	// Hyphens
	];
	for (email, id) in cases {
		assert_eq!(*server.get_id(email)?, ChatPeerId::from(id), "email [{email}] expected to return id [{id}]");
	}
	let cases = [
		"someone@otherdomain.net",
		"@example.com",             // empty local part
		"some@one@example.com",     // more than one '@'
		"someone@example.com.evil",
		"someone@example.org",
	];
	for email in cases {
		let err = server.get_id(email).err()
			.ok_or_else(|| format!("email [{email}] expected to fail")).stack()?;
		assert!(server.get_id(email).unwrap_err().to_string().contains("Doesn't look like address from one of our domains."), "email [{email}] expected to fail");
		assert!(err.to_string().contains("Doesn't look like address from one of our domains."));
	}
	Ok(())
}