Index: src/lib.rs
==================================================================
--- src/lib.rs	
+++ src/lib.rs	
@@ -37,22 +37,26 @@
 	/// Set configuration file location
 	#[arg(short, long, default_value = "smtp2tg.toml")]
 	config: String,
 }
 
-/// Main asynchronous entry point for the application.
+/// Main asynchronous entry point for the application. Runs the gateway using
+/// the configuration selected on the command line.
 ///
-/// Parses command-line arguments, loads configuration, and starts the SMTP
-/// server.
+/// The configuration file must use owner-only permissions. Once configured,
+/// the SMTP server runs until it stops or encounters an error.
 ///
 /// # Errors
-/// Returns an error if configuration is invalid, files are inaccessible, or
-/// server fails to start.
+/// Returns an error if the configuration file is missing, inaccessible,
+/// insecure, malformed, or contains invalid required settings.
+///
+/// # Panics
+/// Panics if configuring or serving the SMTP server fails.
 pub async fn async_main () -> Result<()> {
 	let args = Args::parse();
 	let config_file = Path::new(&args.config);
-	if !config_file.exists() {
+	if !config_file.try_exists().stack()? {
 		bail!("Configuration file not found: {config_file:?}\n\
 			Hint: Ensure the file exists and the path is correct.");
 	};
 	{
 		let meta = metadata(config_file).await.stack()?;
@@ -74,11 +78,11 @@
 		.add_source(config::File::from(config_file))
 		.build()
 		.with_context(|| format!(
 			"Failed to parse configuration file: {config_file:?}\n\
 			Check syntax against smtp2tg.toml.example.\n\
-			Common issues: missing quotes, trailing commas, or invalid types."
+			Common issues: missing quotes, trailing commas in inline tables, or invalid types."
 		))?;
 
 	let listen_on = settings.get_string("listen_on").stack()?;
 	let server_name = settings.get_string("hostname").stack()?;
 	let core = MailServer::new(settings)?;

Index: src/mail.rs
==================================================================
--- src/mail.rs	
+++ src/mail.rs	
@@ -68,11 +68,10 @@
 	/// # Arguments
 	/// * `settings` - Parsed application configuration.
 	///
 	/// # Errors
 	/// Returns an error if required configuration values are missing or invalid.
-	/// server fails to start.
 	pub fn new (settings: config::Config) -> Result<MailServer> {
 		let api_key = settings.get_string("api_key")
 			.context("[smtp2tg.toml] missing \"api_key\" parameter.\n")?;
 		let mut recipients = HashMap::new();
 		for (name, value) in settings.get_table("recipients")

Index: src/telegram.rs
==================================================================
--- src/telegram.rs	
+++ src/telegram.rs	
@@ -109,11 +109,12 @@
 	/// * `to` - Target chat ID.
 	/// * `media` - List of attachments, non-empty.
 	/// * `msg` - Message text (supports HTML formatting).
 	///
 	/// # Returns
-	/// * `Result<()>` - Success or error.
+	/// * `Result<()>` - fails if `media` is empty, problems forming media
+	/// group, request fails.
 	pub async fn sendgroup (&self, to: &ChatPeerId, media: Vec<Attachment>, msg: &str) -> Result<()> {
 		if media.len() > 1 {
 			let mut attach = vec![];
 			let mut pos = media.len();
 			for file in media {