Index: smtp2tg.toml.example
==================================================================
--- smtp2tg.toml.example	
+++ smtp2tg.toml.example	
@@ -6,30 +6,28 @@
 api_gateway = "https://api.telegram.org" # <- note no trailing slash
 
 # where to listen on (sockets are not supported since 0.3.0)
 listen_on = "0.0.0.0:25"
 
-# whether we need to handle unknown adresses
-# - relay: send them to default one
-# - deny: drop them
-unknown = "relay"
-
-# default fields to show in message header
-fields = [ "date", "from", "subject" ]
+# default hostname to use when serving requests
+hostname = "smtp2tg"
 
 # which domains are allowed in addresses
 # this means that any unqualified recipient "somebody" will also match
 # to "somebody@each_domain"
 domains = [ "localhost", "current.hostname" ]
 
 # default recipient, should be specified
-# still can be a user, channel or group
+# still can be a user, channel or group id
 default = 0
+
+# default fields to show in message header
+fields = [ "date", "from", "subject" ]
 
 [recipients]
 # make sure you quote emails, as "@" can't go there unquoted. And by default
-# we need FQDNs
+# we need FQDNs, also keep in mind emails are case insensitive
 "somebody@example.com" = 1 # user id's are positive
 "root" = -1 # group id's are negative
 
 # to look up chat/group id you can use debug settings in Telegram clients,
 # or some bot like @getidsbot or @RawDataBot

Index: src/lib.rs
==================================================================
--- src/lib.rs	
+++ src/lib.rs	
@@ -49,19 +49,22 @@
 /// server fails to start.
 pub async fn async_main () -> Result<()> {
 	let args = Args::parse();
 	let config_file = Path::new(&args.config);
 	if !config_file.exists() {
-		bail!("can't read configuration from {config_file:?}");
+		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()?;
 		if (!0o100600 & meta.permissions().mode()) > 0 {
-			bail!("other users can read or write config file {config_file:?}\n\
-				File permissions: {:o}", meta.permissions().mode());
-		}
-	}
+			bail!("Configuration file permissions are insecure {config_file:?}\n\
+				Current permissions: {:o}\n\
+				Required: 0600 (owner read/write only).\n\
+				Fix with: chmod 600 {config_file:?}",
+				meta.permissions().mode());
+	}	}
 	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()?
@@ -68,12 +71,15 @@
 		.set_default("domains", vec!["localhost",
 			hostname::get().context("Failed to get current hostname")?
 			.to_str().context("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"))?;
+		.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."
+		))?;
 
 	let listen_on = settings.get_string("listen_on").stack()?;
 	let server_name = settings.get_string("hostname").stack()?;
 	let core = MailServer::new(settings)?;
 	let mut server = mailin_embedded::Server::new(core);

Index: src/mail.rs
==================================================================
--- src/mail.rs	
+++ src/mail.rs	
@@ -57,10 +57,11 @@
 	data: Vec<u8>,
 	headers: Option<SomeHeaders>,
 	tg: Arc<TelegramTransport>,
 	fields: HashSet<String>,
 	address: Regex,
+	domains: HashSet<String>,
 }
 
 impl MailServer {
 	/// Initializes the mail server: sets up the Telegram API client and
 	/// validates all required configuration values.
@@ -93,27 +94,29 @@
 		for domain in extra_domains {
 			let domain = domain.to_string().to_lowercase();
 			if RE_DOMAIN.is_match(&domain) {
 				domains.insert(domain);
 			} else {
-				bail!("[smtp2tg.toml] can't check domains in \"domains\": {domain}");
-			}
-		}
+				bail!("Invalid domain in configuration: '{domain}'\n\
+					Domains must be valid (e.g., 'example.com', 'localhost').\n\
+					Check 'domains' array in smtp2tg.toml.");
+		}	}
 		if domains.is_empty() {
 			bail!("No domains, need at least one: default `localhost` would do.");
 		}
-		let domains = domains.into_iter().map(|s| escape(&s))
+		let re_domains = domains.iter().map(|s| escape(s))
 			.collect::<Vec<String>>().join("|");
-		let address = RegexBuilder::new(&format!("^[a-z0-9][a-z0-9.-]*(@({domains}))?$"))
+		let address = RegexBuilder::new(&format!("^[a-z0-9][a-z0-9.-]*(@({re_domains}))?$"))
 			.case_insensitive(true).build().stack()?;
 
 		Ok(MailServer {
 			data: vec!(),
 			headers: None,
 			tg,
 			fields,
 			address,
+			domains,
 		})
 	}
 
 	/// Retrieves the Telegram chat ID for a given email address, checks that
 	/// used domain is allowed.
@@ -126,13 +129,12 @@
 	///   not found.
 	pub fn get_id (&self, name: &str) -> Result<&ChatPeerId> {
 		if self.address.is_match(name) {
 			Ok(self.tg.get(name).unwrap_or(&self.tg.default))
 		} else {
-			bail!("Doesn't look like address from one of our domains.");
-		}
-	}
+			bail!("Email address {name:?} is not from an allowed domain.");
+	}	}
 
 	/// Attempt to deliver one message
 	async fn relay_mail (&self) -> Result<()> {
 		if let Some(headers) = &self.headers {
 			let mail = mail_parser::MessageParser::new().parse(&self.data)

Index: src/telegram.rs
==================================================================
--- src/telegram.rs	
+++ src/telegram.rs	
@@ -94,11 +94,11 @@
 	///
 	/// # Errors
 	/// Returns an error if `name` is not configured.
 	pub fn get (&self, name: &str) -> Result<&ChatPeerId> {
 		self.recipients.get(&name.to_lowercase())
-			.with_context(|| format!("Recipient \"{name}\" not found in configuration"))
+			.with_context(|| format!("Recipient {name:?} not found in configuration"))
 	}
 
 	/// Sends a text message to a specified chat.
 	///
 	/// # Arguments

Index: src/utils.rs
==================================================================
--- src/utils.rs	
+++ src/utils.rs	
@@ -46,10 +46,9 @@
 ///
 /// # Errors
 /// Returns an error if the text contains Telegram closing tags (`</pre>`, `</code>`).
 pub fn validate <'a>(text: &'a str) -> Result<Cow<'a, str>> {
 	if RE_CLOSING.is_match(text) {
-		bail!("Telegram closing tag found.");
+		bail!("Text contains a Telegram closing tag (e.g., </pre>, </code>).");
 	} else {
 		Ok(encode_text(text))
-	}
-}
+}	}