512369f93e 2026-08-01 1: //! SMTP server implementation for receiving and processing emails.
512369f93e 2026-08-01 2: //!
512369f93e 2026-08-01 3: //! This module handles SMTP connections, email parsing, and forwarding to
512369f93e 2026-08-01 4: //! Telegram.
512369f93e 2026-08-01 5:
f5ed284f8c 2025-06-21 6: use crate::{
f5ed284f8c 2025-06-21 7: Cursor,
0f47e23e21 2026-01-12 8: telegram::TelegramTransport,
f5ed284f8c 2025-06-21 9: utils::{
f5ed284f8c 2025-06-21 10: Attachment,
f5ed284f8c 2025-06-21 11: RE_DOMAIN,
0f47e23e21 2026-01-12 12: validate,
f5ed284f8c 2025-06-21 13: },
f5ed284f8c 2025-06-21 14: };
f5ed284f8c 2025-06-21 15:
f5ed284f8c 2025-06-21 16: use std::{
f5ed284f8c 2025-06-21 17: collections::{
f5ed284f8c 2025-06-21 18: HashMap,
f5ed284f8c 2025-06-21 19: HashSet,
f5ed284f8c 2025-06-21 20: },
f5ed284f8c 2025-06-21 21: io::Error,
072229b5bf 2026-01-01 22: sync::Arc,
f5ed284f8c 2025-06-21 23: };
f5ed284f8c 2025-06-21 24:
14ef340959 2026-01-01 25: use async_compat::Compat;
f5ed284f8c 2025-06-21 26: use mailin_embedded::{
f5ed284f8c 2025-06-21 27: Response,
f5ed284f8c 2025-06-21 28: response::{
f5ed284f8c 2025-06-21 29: INTERNAL_ERROR,
f5ed284f8c 2025-06-21 30: INVALID_CREDENTIALS,
f5ed284f8c 2025-06-21 31: NO_MAILBOX,
f5ed284f8c 2025-06-21 32: OK
f5ed284f8c 2025-06-21 33: },
f5ed284f8c 2025-06-21 34: };
f5ed284f8c 2025-06-21 35: use regex::{
f5ed284f8c 2025-06-21 36: Regex,
158c9cffc6 2026-08-01 37: RegexBuilder,
f5ed284f8c 2025-06-21 38: escape,
a044f68fa7 2025-08-23 39: };
a044f68fa7 2025-08-23 40: use stacked_errors::{
a044f68fa7 2025-08-23 41: Result,
a044f68fa7 2025-08-23 42: StackableErr,
a044f68fa7 2025-08-23 43: bail,
f5ed284f8c 2025-06-21 44: };
f5ed284f8c 2025-06-21 45: use tgbot::types::ChatPeerId;
f5ed284f8c 2025-06-21 46:
f5ed284f8c 2025-06-21 47: /// `SomeHeaders` object to store data through SMTP session
f5ed284f8c 2025-06-21 48: #[derive(Clone, Debug)]
f5ed284f8c 2025-06-21 49: struct SomeHeaders {
f5ed284f8c 2025-06-21 50: from: String,
f5ed284f8c 2025-06-21 51: to: Vec<String>,
f5ed284f8c 2025-06-21 52: }
f5ed284f8c 2025-06-21 53:
f5ed284f8c 2025-06-21 54: /// `MailServer` Central object with TG api and configuration
f5ed284f8c 2025-06-21 55: #[derive(Clone, Debug)]
f5ed284f8c 2025-06-21 56: pub struct MailServer {
f5ed284f8c 2025-06-21 57: data: Vec<u8>,
f5ed284f8c 2025-06-21 58: headers: Option<SomeHeaders>,
f5ed284f8c 2025-06-21 59: tg: Arc<TelegramTransport>,
f5ed284f8c 2025-06-21 60: fields: HashSet<String>,
f5ed284f8c 2025-06-21 61: address: Regex,
0acb6536ae 2026-09-10 62: domains: HashSet<String>,
f5ed284f8c 2025-06-21 63: }
f5ed284f8c 2025-06-21 64:
f5ed284f8c 2025-06-21 65: impl MailServer {
1723b63d69 2026-08-01 66: /// Initializes the mail server: sets up the Telegram API client and
1723b63d69 2026-08-01 67: /// validates all required configuration values.
512369f93e 2026-08-01 68: ///
1723b63d69 2026-08-01 69: /// # Arguments
1723b63d69 2026-08-01 70: /// * `settings` - Parsed application configuration.
512369f93e 2026-08-01 71: ///
512369f93e 2026-08-01 72: /// # Errors
1723b63d69 2026-08-01 73: /// Returns an error if required configuration values are missing or invalid.
512369f93e 2026-08-01 74: /// server fails to start.
1723b63d69 2026-08-01 75: pub fn new (settings: config::Config) -> Result<MailServer> {
f5ed284f8c 2025-06-21 76: let api_key = settings.get_string("api_key")
f5ed284f8c 2025-06-21 77: .context("[smtp2tg.toml] missing \"api_key\" parameter.\n")?;
f5ed284f8c 2025-06-21 78: let mut recipients = HashMap::new();
f5ed284f8c 2025-06-21 79: for (name, value) in settings.get_table("recipients")
98c5a42df0 2026-08-01 80: .context("[smtp2tg.toml] missing table \"recipients\".\n")?
f5ed284f8c 2025-06-21 81: {
f5ed284f8c 2025-06-21 82: let value = value.into_int()
f5ed284f8c 2025-06-21 83: .context("[smtp2tg.toml] \"recipient\" table values should be integers.\n")?;
aaa78fed23 2026-08-01 84: recipients.insert(name.to_lowercase(), value);
14ef340959 2026-01-01 85: }
14ef340959 2026-01-01 86:
14ef340959 2026-01-01 87: let tg = Arc::new(TelegramTransport::new(api_key, recipients, &settings)?);
14ef340959 2026-01-01 88: let fields = HashSet::<String>::from_iter(settings.get_array("fields")
98c5a42df0 2026-08-01 89: .context("[smtp2tg.toml] \"fields\" should be an array")?
98c5a42df0 2026-08-01 90: .iter().map(|x| x.clone().into_string().context("should be strings"))
98c5a42df0 2026-08-01 91: .collect::<Result<Vec<String>>>()?);
f5ed284f8c 2025-06-21 92: let mut domains: HashSet<String> = HashSet::new();
a044f68fa7 2025-08-23 93: let extra_domains = settings.get_array("domains").stack()?;
f5ed284f8c 2025-06-21 94: for domain in extra_domains {
f5ed284f8c 2025-06-21 95: let domain = domain.to_string().to_lowercase();
f5ed284f8c 2025-06-21 96: if RE_DOMAIN.is_match(&domain) {
f5ed284f8c 2025-06-21 97: domains.insert(domain);
f5ed284f8c 2025-06-21 98: } else {
0acb6536ae 2026-09-10 99: bail!("Invalid domain in configuration: '{domain}'\n\
0acb6536ae 2026-09-10 100: Domains must be valid (e.g., 'example.com', 'localhost').\n\
0acb6536ae 2026-09-10 101: Check 'domains' array in smtp2tg.toml.");
0acb6536ae 2026-09-10 102: } }
98c5a42df0 2026-08-01 103: if domains.is_empty() {
98c5a42df0 2026-08-01 104: bail!("No domains, need at least one: default `localhost` would do.");
f5ed284f8c 2025-06-21 105: }
0acb6536ae 2026-09-10 106: let re_domains = domains.iter().map(|s| escape(s))
f5ed284f8c 2025-06-21 107: .collect::<Vec<String>>().join("|");
0acb6536ae 2026-09-10 108: let address = RegexBuilder::new(&format!("^[a-z0-9][a-z0-9.-]*(@({re_domains}))?$"))
158c9cffc6 2026-08-01 109: .case_insensitive(true).build().stack()?;
f5ed284f8c 2025-06-21 110:
f5ed284f8c 2025-06-21 111: Ok(MailServer {
f5ed284f8c 2025-06-21 112: data: vec!(),
f5ed284f8c 2025-06-21 113: headers: None,
f5ed284f8c 2025-06-21 114: tg,
f5ed284f8c 2025-06-21 115: fields,
f5ed284f8c 2025-06-21 116: address,
0acb6536ae 2026-09-10 117: domains,
f5ed284f8c 2025-06-21 118: })
f5ed284f8c 2025-06-21 119: }
f5ed284f8c 2025-06-21 120:
512369f93e 2026-08-01 121: /// Retrieves the Telegram chat ID for a given email address, checks that
512369f93e 2026-08-01 122: /// used domain is allowed.
512369f93e 2026-08-01 123: ///
512369f93e 2026-08-01 124: /// # Arguments
1723b63d69 2026-08-01 125: /// * `name` - Email address or username to look up.
512369f93e 2026-08-01 126: ///
512369f93e 2026-08-01 127: /// # Returns
512369f93e 2026-08-01 128: /// * `Result<ChatPeerId>` - Telegram chat ID for the address, or default if
512369f93e 2026-08-01 129: /// not found.
f748e99b70 2026-08-01 130: pub fn get_id (&self, name: &str) -> Result<&ChatPeerId> {
f748e99b70 2026-08-01 131: if self.address.is_match(name) {
1723b63d69 2026-08-01 132: Ok(self.tg.get(name).unwrap_or(&self.tg.default))
f748e99b70 2026-08-01 133: } else {
0acb6536ae 2026-09-10 134: bail!("Email address {name:?} is not from an allowed domain.");
0acb6536ae 2026-09-10 135: } }
f5ed284f8c 2025-06-21 136:
f5ed284f8c 2025-06-21 137: /// Attempt to deliver one message
f5ed284f8c 2025-06-21 138: async fn relay_mail (&self) -> Result<()> {
f5ed284f8c 2025-06-21 139: if let Some(headers) = &self.headers {
f5ed284f8c 2025-06-21 140: let mail = mail_parser::MessageParser::new().parse(&self.data)
f5ed284f8c 2025-06-21 141: .context("Failed to parse mail.")?;
f5ed284f8c 2025-06-21 142:
f5ed284f8c 2025-06-21 143: // Adding all known addresses to recipient list, for anyone else adding default
f5ed284f8c 2025-06-21 144: // Also if list is empty also adding default
f5ed284f8c 2025-06-21 145: let mut rcpt: HashSet<&ChatPeerId> = HashSet::new();
158c9cffc6 2026-08-01 146: if headers.to.is_empty() {
f5ed284f8c 2025-06-21 147: bail!("Relaying is disabled, and there's no destination address");
f5ed284f8c 2025-06-21 148: }
f5ed284f8c 2025-06-21 149: for item in &headers.to {
f5ed284f8c 2025-06-21 150: rcpt.insert(self.get_id(item)?);
f5ed284f8c 2025-06-21 151: };
f5ed284f8c 2025-06-21 152: if rcpt.is_empty() {
f5ed284f8c 2025-06-21 153: self.tg.debug("No recipient or envelope address.").await?;
f5ed284f8c 2025-06-21 154: rcpt.insert(&self.tg.default);
f5ed284f8c 2025-06-21 155: };
f5ed284f8c 2025-06-21 156:
0f47e23e21 2026-01-12 157: // preparing message header
0f47e23e21 2026-01-12 158: let mut reply: Vec<String> = vec!["<blockquote expandable>".into()];
14ef340959 2026-01-01 159: if self.fields.contains("subject") {
14ef340959 2026-01-01 160: if let Some(subject) = mail.subject() {
0f47e23e21 2026-01-12 161: reply.push(format!("<u><i>Subject:</i></u> <code>{}</code>", validate(subject).stack()?));
14ef340959 2026-01-01 162: } else if let Some(thread) = mail.thread_name() {
0f47e23e21 2026-01-12 163: reply.push(format!("<u><i>Thread:</i></u> <code>{}</code>", validate(thread).stack()?));
14ef340959 2026-01-01 164: }
14ef340959 2026-01-01 165: }
14ef340959 2026-01-01 166: // do we need to replace spaces here?
14ef340959 2026-01-01 167: if self.fields.contains("from") {
0f47e23e21 2026-01-12 168: reply.push(format!("<u><i>From:</i></u> <code>{}</code>", validate(&headers.from).stack()?));
0f47e23e21 2026-01-12 169: }
0f47e23e21 2026-01-12 170: if self.fields.contains("date")
0f47e23e21 2026-01-12 171: && let Some(date) = mail.date()
0f47e23e21 2026-01-12 172: {
0f47e23e21 2026-01-12 173: reply.push(format!("<u><i>Date:</i></u> <code>{date}</code>"));
0f47e23e21 2026-01-12 174: }
0f47e23e21 2026-01-12 175: reply.push("</blockquote><pre>".into());
c996f5c871 2026-01-12 176: let reply = reply.join("\n");
f5ed284f8c 2025-06-21 177:
f5ed284f8c 2025-06-21 178: let html_parts = mail.html_body_count();
f5ed284f8c 2025-06-21 179: let text_parts = mail.text_body_count();
f5ed284f8c 2025-06-21 180: let attachments = mail.attachment_count();
f5ed284f8c 2025-06-21 181: if html_parts != text_parts {
f5ed284f8c 2025-06-21 182: self.tg.debug(&format!("Hm, we have {html_parts} HTML parts and {text_parts} text parts.")).await?;
f5ed284f8c 2025-06-21 183: }
f5ed284f8c 2025-06-21 184: //let mut html_num = 0;
f5ed284f8c 2025-06-21 185: let mut text_num = 0;
f5ed284f8c 2025-06-21 186: let mut file_num = 0;
f5ed284f8c 2025-06-21 187: // let's display first html or text part as body
c996f5c871 2026-01-12 188: let mut body: String = "".into();
f5ed284f8c 2025-06-21 189: /*
f5ed284f8c 2025-06-21 190: * actually I don't wanna parse that html stuff
f5ed284f8c 2025-06-21 191: if html_parts > 0 {
a044f68fa7 2025-08-23 192: let text = mail.body_html(0).stack()?;
f5ed284f8c 2025-06-21 193: if text.len() < 4096 - header_size {
f5ed284f8c 2025-06-21 194: body = text;
f5ed284f8c 2025-06-21 195: html_num = 1;
f5ed284f8c 2025-06-21 196: }
f5ed284f8c 2025-06-21 197: };
f5ed284f8c 2025-06-21 198: */
f5ed284f8c 2025-06-21 199: if body.is_empty() && text_parts > 0 {
f5ed284f8c 2025-06-21 200: let text = mail.body_text(0)
c996f5c871 2026-01-12 201: .context("Failed to extract text from message")?
c996f5c871 2026-01-12 202: .replace("\r\n", "\n");
db04f7359b 2026-01-18 203: let text = validate(&text).stack()?;
c996f5c871 2026-01-12 204: // 6:
c996f5c871 2026-01-12 205: // - (headers)
0f47e23e21 2026-01-12 206: // - (mail text)
0f47e23e21 2026-01-12 207: // - 6: </pre>
6ce625a569 2026-01-12 208: if text.len() < 4096 - ( reply.len() + 6 ) {
db04f7359b 2026-01-18 209: body = text.to_string();
f5ed284f8c 2025-06-21 210: text_num = 1;
f5ed284f8c 2025-06-21 211: }
f5ed284f8c 2025-06-21 212: };
db04f7359b 2026-01-18 213: let msg = format!("{}{}</pre>", reply, body);
f5ed284f8c 2025-06-21 214:
f5ed284f8c 2025-06-21 215: // and let's collect all other attachment parts
f5ed284f8c 2025-06-21 216: let mut files_to_send = vec![];
f5ed284f8c 2025-06-21 217: /*
f5ed284f8c 2025-06-21 218: * let's just skip html parts for now, they just duplicate text?
f5ed284f8c 2025-06-21 219: while html_num < html_parts {
a044f68fa7 2025-08-23 220: files_to_send.push(mail.html_part(html_num).stack()?);
f5ed284f8c 2025-06-21 221: html_num += 1;
f5ed284f8c 2025-06-21 222: }
f5ed284f8c 2025-06-21 223: */
f5ed284f8c 2025-06-21 224: while text_num < text_parts {
a044f68fa7 2025-08-23 225: files_to_send.push(mail.text_part(text_num.try_into().stack()?)
f5ed284f8c 2025-06-21 226: .context("Failed to get text part from message.")?);
f5ed284f8c 2025-06-21 227: text_num += 1;
f5ed284f8c 2025-06-21 228: }
f5ed284f8c 2025-06-21 229: while file_num < attachments {
a044f68fa7 2025-08-23 230: files_to_send.push(mail.attachment(file_num.try_into().stack()?)
f5ed284f8c 2025-06-21 231: .context("Failed to get file part from message.")?);
f5ed284f8c 2025-06-21 232: file_num += 1;
f5ed284f8c 2025-06-21 233: }
f5ed284f8c 2025-06-21 234:
f5ed284f8c 2025-06-21 235: for chat in rcpt {
f5ed284f8c 2025-06-21 236: if !files_to_send.is_empty() {
f5ed284f8c 2025-06-21 237: let mut files = vec![];
f5ed284f8c 2025-06-21 238: // let mut first_one = true;
f5ed284f8c 2025-06-21 239: for chunk in &files_to_send {
f5ed284f8c 2025-06-21 240: let data: Vec<u8> = chunk.contents().to_vec();
f5ed284f8c 2025-06-21 241: let mut filename: Option<String> = None;
f5ed284f8c 2025-06-21 242: for header in chunk.headers() {
f5ed284f8c 2025-06-21 243: if header.name() == "Content-Type" {
f5ed284f8c 2025-06-21 244: match header.value() {
f5ed284f8c 2025-06-21 245: mail_parser::HeaderValue::ContentType(contenttype) => {
f5ed284f8c 2025-06-21 246: if let Some(fname) = contenttype.attribute("name") {
f5ed284f8c 2025-06-21 247: filename = Some(fname.to_owned());
f5ed284f8c 2025-06-21 248: }
f5ed284f8c 2025-06-21 249: },
f5ed284f8c 2025-06-21 250: _ => {
f5ed284f8c 2025-06-21 251: self.tg.debug("Attachment has bad ContentType header.").await?;
f5ed284f8c 2025-06-21 252: },
f5ed284f8c 2025-06-21 253: };
f5ed284f8c 2025-06-21 254: };
f5ed284f8c 2025-06-21 255: };
f5ed284f8c 2025-06-21 256: let filename = if let Some(fname) = filename {
f5ed284f8c 2025-06-21 257: fname
f5ed284f8c 2025-06-21 258: } else {
f5ed284f8c 2025-06-21 259: "Attachment.txt".into()
f5ed284f8c 2025-06-21 260: };
f5ed284f8c 2025-06-21 261: files.push(Attachment {
f5ed284f8c 2025-06-21 262: data: Cursor::new(data),
f5ed284f8c 2025-06-21 263: name: filename,
f5ed284f8c 2025-06-21 264: });
f5ed284f8c 2025-06-21 265: }
f5ed284f8c 2025-06-21 266: self.tg.sendgroup(chat, files, &msg).await?;
f5ed284f8c 2025-06-21 267: } else {
f5ed284f8c 2025-06-21 268: self.tg.send(chat, &msg).await?;
f5ed284f8c 2025-06-21 269: }
f5ed284f8c 2025-06-21 270: }
f5ed284f8c 2025-06-21 271: } else {
f5ed284f8c 2025-06-21 272: bail!("Required headers were not found.");
f5ed284f8c 2025-06-21 273: }
f5ed284f8c 2025-06-21 274: Ok(())
f5ed284f8c 2025-06-21 275: }
f5ed284f8c 2025-06-21 276: }
f5ed284f8c 2025-06-21 277:
512369f93e 2026-08-01 278: /// SMTP handler implementation for mailin-embedded.
f5ed284f8c 2025-06-21 279: impl mailin_embedded::Handler for MailServer {
f5ed284f8c 2025-06-21 280: /// Just deny login auth
f5ed284f8c 2025-06-21 281: fn auth_login (&mut self, _username: &str, _password: &str) -> Response {
f5ed284f8c 2025-06-21 282: INVALID_CREDENTIALS
f5ed284f8c 2025-06-21 283: }
f5ed284f8c 2025-06-21 284:
f5ed284f8c 2025-06-21 285: /// Just deny plain auth
f5ed284f8c 2025-06-21 286: fn auth_plain (&mut self, _authorization_id: &str, _authentication_id: &str, _password: &str) -> Response {
f5ed284f8c 2025-06-21 287: INVALID_CREDENTIALS
f5ed284f8c 2025-06-21 288: }
f5ed284f8c 2025-06-21 289:
f5ed284f8c 2025-06-21 290: /// Verify whether address is deliverable
f5ed284f8c 2025-06-21 291: fn rcpt (&mut self, to: &str) -> Response {
158c9cffc6 2026-08-01 292: if self.get_id(to).is_ok() {
f5ed284f8c 2025-06-21 293: OK
f5ed284f8c 2025-06-21 294: } else {
1723b63d69 2026-08-01 295: NO_MAILBOX
f5ed284f8c 2025-06-21 296: }
f5ed284f8c 2025-06-21 297: }
f5ed284f8c 2025-06-21 298:
f5ed284f8c 2025-06-21 299: /// Save headers we need
f5ed284f8c 2025-06-21 300: fn data_start (&mut self, _domain: &str, from: &str, _is8bit: bool, to: &[String]) -> Response {
f5ed284f8c 2025-06-21 301: self.headers = Some(SomeHeaders{
f5ed284f8c 2025-06-21 302: from: from.to_string(),
f5ed284f8c 2025-06-21 303: to: to.to_vec(),
f5ed284f8c 2025-06-21 304: });
f5ed284f8c 2025-06-21 305: OK
f5ed284f8c 2025-06-21 306: }
f5ed284f8c 2025-06-21 307:
f5ed284f8c 2025-06-21 308: /// Save chunk(?) of data
a044f68fa7 2025-08-23 309: fn data (&mut self, buf: &[u8]) -> std::result::Result<(), Error> {
f5ed284f8c 2025-06-21 310: self.data.append(buf.to_vec().as_mut());
f5ed284f8c 2025-06-21 311: Ok(())
f5ed284f8c 2025-06-21 312: }
f5ed284f8c 2025-06-21 313:
f5ed284f8c 2025-06-21 314: /// Attempt to send email, return temporary error if that fails
f5ed284f8c 2025-06-21 315: fn data_end (&mut self) -> Response {
f5ed284f8c 2025-06-21 316: let mut result = OK;
14ef340959 2026-01-01 317: smol::block_on(Compat::new(async {
f5ed284f8c 2025-06-21 318: // relay mail
f5ed284f8c 2025-06-21 319: if let Err(err) = self.relay_mail().await {
f5ed284f8c 2025-06-21 320: result = INTERNAL_ERROR;
f5ed284f8c 2025-06-21 321: // in case that fails - inform default recipient
700254f838 2026-01-18 322: if let Err(err) = self.tg.debug(&format!("Sending emails failed:\n{err:}")).await {
f5ed284f8c 2025-06-21 323: // in case that also fails - write some logs and bail
f5ed284f8c 2025-06-21 324: eprintln!("{err:?}");
f5ed284f8c 2025-06-21 325: };
f5ed284f8c 2025-06-21 326: };
14ef340959 2026-01-01 327: }));
f5ed284f8c 2025-06-21 328: // clear - just in case
f5ed284f8c 2025-06-21 329: self.data = vec![];
f5ed284f8c 2025-06-21 330: self.headers = None;
f5ed284f8c 2025-06-21 331: result
f5ed284f8c 2025-06-21 332: }
f5ed284f8c 2025-06-21 333: }