78b11b0319 2026-08-01 1: //! SMTP server implementation for receiving and processing emails.
78b11b0319 2026-08-01 2: //!
78b11b0319 2026-08-01 3: //! This module handles SMTP connections, email parsing, and forwarding to
78b11b0319 2026-08-01 4: //! Telegram.
78b11b0319 2026-08-01 5:
f5ed284f8c 2025-06-21 6: use crate::{
f5ed284f8c 2025-06-21 7: Cursor,
d87e80b9be 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,
d87e80b9be 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,
78b11b0319 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,
f5ed284f8c 2025-06-21 62: }
f5ed284f8c 2025-06-21 63:
f5ed284f8c 2025-06-21 64: impl MailServer {
78b11b0319 2026-08-01 65: /// Initializes the mail server: sets up the Telegram API client and
78b11b0319 2026-08-01 66: /// validates all required configuration values.
78b11b0319 2026-08-01 67: ///
78b11b0319 2026-08-01 68: /// # Arguments
78b11b0319 2026-08-01 69: /// * `settings` - Parsed application configuration.
78b11b0319 2026-08-01 70: ///
78b11b0319 2026-08-01 71: /// # Errors
78b11b0319 2026-08-01 72: /// Returns an error if required configuration values are missing or invalid.
78b11b0319 2026-08-01 73: /// server fails to start.
78b11b0319 2026-08-01 74: pub fn new (settings: config::Config) -> Result<MailServer> {
f5ed284f8c 2025-06-21 75: let api_key = settings.get_string("api_key")
f5ed284f8c 2025-06-21 76: .context("[smtp2tg.toml] missing \"api_key\" parameter.\n")?;
f5ed284f8c 2025-06-21 77: let mut recipients = HashMap::new();
f5ed284f8c 2025-06-21 78: for (name, value) in settings.get_table("recipients")
78b11b0319 2026-08-01 79: .context("[smtp2tg.toml] missing table \"recipients\".\n")?
f5ed284f8c 2025-06-21 80: {
f5ed284f8c 2025-06-21 81: let value = value.into_int()
f5ed284f8c 2025-06-21 82: .context("[smtp2tg.toml] \"recipient\" table values should be integers.\n")?;
78b11b0319 2026-08-01 83: recipients.insert(name.to_lowercase(), value);
f5ed284f8c 2025-06-21 84: }
f5ed284f8c 2025-06-21 85:
14ef340959 2026-01-01 86: let tg = Arc::new(TelegramTransport::new(api_key, recipients, &settings)?);
f5ed284f8c 2025-06-21 87: let fields = HashSet::<String>::from_iter(settings.get_array("fields")
78b11b0319 2026-08-01 88: .context("[smtp2tg.toml] \"fields\" should be an array")?
78b11b0319 2026-08-01 89: .iter().map(|x| x.clone().into_string().context("should be strings"))
78b11b0319 2026-08-01 90: .collect::<Result<Vec<String>>>()?);
f5ed284f8c 2025-06-21 91: let mut domains: HashSet<String> = HashSet::new();
a044f68fa7 2025-08-23 92: let extra_domains = settings.get_array("domains").stack()?;
f5ed284f8c 2025-06-21 93: for domain in extra_domains {
f5ed284f8c 2025-06-21 94: let domain = domain.to_string().to_lowercase();
f5ed284f8c 2025-06-21 95: if RE_DOMAIN.is_match(&domain) {
f5ed284f8c 2025-06-21 96: domains.insert(domain);
f5ed284f8c 2025-06-21 97: } else {
78b11b0319 2026-08-01 98: bail!("[smtp2tg.toml] can't check domains in \"domains\": {domain}");
f5ed284f8c 2025-06-21 99: }
78b11b0319 2026-08-01 100: }
78b11b0319 2026-08-01 101: if domains.is_empty() {
78b11b0319 2026-08-01 102: bail!("No domains, need at least one: default `localhost` would do.");
f5ed284f8c 2025-06-21 103: }
f5ed284f8c 2025-06-21 104: let domains = domains.into_iter().map(|s| escape(&s))
f5ed284f8c 2025-06-21 105: .collect::<Vec<String>>().join("|");
78b11b0319 2026-08-01 106: let address = RegexBuilder::new(&format!("^[a-z0-9][a-z0-9.-]*(@({domains}))?$"))
78b11b0319 2026-08-01 107: .case_insensitive(true).build().stack()?;
f5ed284f8c 2025-06-21 108:
f5ed284f8c 2025-06-21 109: Ok(MailServer {
f5ed284f8c 2025-06-21 110: data: vec!(),
f5ed284f8c 2025-06-21 111: headers: None,
f5ed284f8c 2025-06-21 112: tg,
f5ed284f8c 2025-06-21 113: fields,
f5ed284f8c 2025-06-21 114: address,
f5ed284f8c 2025-06-21 115: })
f5ed284f8c 2025-06-21 116: }
f5ed284f8c 2025-06-21 117:
78b11b0319 2026-08-01 118: /// Retrieves the Telegram chat ID for a given email address, checks that
78b11b0319 2026-08-01 119: /// used domain is allowed.
78b11b0319 2026-08-01 120: ///
78b11b0319 2026-08-01 121: /// # Arguments
78b11b0319 2026-08-01 122: /// * `name` - Email address or username to look up.
78b11b0319 2026-08-01 123: ///
78b11b0319 2026-08-01 124: /// # Returns
78b11b0319 2026-08-01 125: /// * `Result<ChatPeerId>` - Telegram chat ID for the address, or default if
78b11b0319 2026-08-01 126: /// not found.
78b11b0319 2026-08-01 127: pub fn get_id (&self, name: &str) -> Result<&ChatPeerId> {
78b11b0319 2026-08-01 128: if self.address.is_match(name) {
78b11b0319 2026-08-01 129: Ok(self.tg.get(name).unwrap_or(&self.tg.default))
78b11b0319 2026-08-01 130: } else {
78b11b0319 2026-08-01 131: bail!("Doesn't look like address from one of our domains.");
f5ed284f8c 2025-06-21 132: }
f5ed284f8c 2025-06-21 133: }
f5ed284f8c 2025-06-21 134:
f5ed284f8c 2025-06-21 135: /// Attempt to deliver one message
f5ed284f8c 2025-06-21 136: async fn relay_mail (&self) -> Result<()> {
f5ed284f8c 2025-06-21 137: if let Some(headers) = &self.headers {
f5ed284f8c 2025-06-21 138: let mail = mail_parser::MessageParser::new().parse(&self.data)
f5ed284f8c 2025-06-21 139: .context("Failed to parse mail.")?;
f5ed284f8c 2025-06-21 140:
f5ed284f8c 2025-06-21 141: // Adding all known addresses to recipient list, for anyone else adding default
f5ed284f8c 2025-06-21 142: // Also if list is empty also adding default
f5ed284f8c 2025-06-21 143: let mut rcpt: HashSet<&ChatPeerId> = HashSet::new();
78b11b0319 2026-08-01 144: if headers.to.is_empty() {
f5ed284f8c 2025-06-21 145: bail!("Relaying is disabled, and there's no destination address");
f5ed284f8c 2025-06-21 146: }
f5ed284f8c 2025-06-21 147: for item in &headers.to {
f5ed284f8c 2025-06-21 148: rcpt.insert(self.get_id(item)?);
f5ed284f8c 2025-06-21 149: };
f5ed284f8c 2025-06-21 150: if rcpt.is_empty() {
f5ed284f8c 2025-06-21 151: self.tg.debug("No recipient or envelope address.").await?;
f5ed284f8c 2025-06-21 152: rcpt.insert(&self.tg.default);
f5ed284f8c 2025-06-21 153: };
f5ed284f8c 2025-06-21 154:
d87e80b9be 2026-01-12 155: // preparing message header
d87e80b9be 2026-01-12 156: let mut reply: Vec<String> = vec!["<blockquote expandable>".into()];
14ef340959 2026-01-01 157: if self.fields.contains("subject") {
14ef340959 2026-01-01 158: if let Some(subject) = mail.subject() {
d87e80b9be 2026-01-12 159: reply.push(format!("<u><i>Subject:</i></u> <code>{}</code>", validate(subject).stack()?));
14ef340959 2026-01-01 160: } else if let Some(thread) = mail.thread_name() {
d87e80b9be 2026-01-12 161: reply.push(format!("<u><i>Thread:</i></u> <code>{}</code>", validate(thread).stack()?));
14ef340959 2026-01-01 162: }
14ef340959 2026-01-01 163: }
14ef340959 2026-01-01 164: // do we need to replace spaces here?
14ef340959 2026-01-01 165: if self.fields.contains("from") {
d87e80b9be 2026-01-12 166: reply.push(format!("<u><i>From:</i></u> <code>{}</code>", validate(&headers.from).stack()?));
d87e80b9be 2026-01-12 167: }
d87e80b9be 2026-01-12 168: if self.fields.contains("date")
d87e80b9be 2026-01-12 169: && let Some(date) = mail.date()
d87e80b9be 2026-01-12 170: {
d87e80b9be 2026-01-12 171: reply.push(format!("<u><i>Date:</i></u> <code>{date}</code>"));
d87e80b9be 2026-01-12 172: }
d87e80b9be 2026-01-12 173: reply.push("</blockquote><pre>".into());
d87e80b9be 2026-01-12 174: let reply = reply.join("\n");
f5ed284f8c 2025-06-21 175:
f5ed284f8c 2025-06-21 176: let html_parts = mail.html_body_count();
f5ed284f8c 2025-06-21 177: let text_parts = mail.text_body_count();
f5ed284f8c 2025-06-21 178: let attachments = mail.attachment_count();
f5ed284f8c 2025-06-21 179: if html_parts != text_parts {
f5ed284f8c 2025-06-21 180: self.tg.debug(&format!("Hm, we have {html_parts} HTML parts and {text_parts} text parts.")).await?;
f5ed284f8c 2025-06-21 181: }
f5ed284f8c 2025-06-21 182: //let mut html_num = 0;
f5ed284f8c 2025-06-21 183: let mut text_num = 0;
f5ed284f8c 2025-06-21 184: let mut file_num = 0;
f5ed284f8c 2025-06-21 185: // let's display first html or text part as body
d87e80b9be 2026-01-12 186: let mut body: String = "".into();
f5ed284f8c 2025-06-21 187: /*
f5ed284f8c 2025-06-21 188: * actually I don't wanna parse that html stuff
f5ed284f8c 2025-06-21 189: if html_parts > 0 {
a044f68fa7 2025-08-23 190: let text = mail.body_html(0).stack()?;
f5ed284f8c 2025-06-21 191: if text.len() < 4096 - header_size {
f5ed284f8c 2025-06-21 192: body = text;
f5ed284f8c 2025-06-21 193: html_num = 1;
f5ed284f8c 2025-06-21 194: }
f5ed284f8c 2025-06-21 195: };
f5ed284f8c 2025-06-21 196: */
f5ed284f8c 2025-06-21 197: if body.is_empty() && text_parts > 0 {
f5ed284f8c 2025-06-21 198: let text = mail.body_text(0)
d87e80b9be 2026-01-12 199: .context("Failed to extract text from message")?
d87e80b9be 2026-01-12 200: .replace("\r\n", "\n");
1c10bccb4e 2026-01-18 201: let text = validate(&text).stack()?;
d87e80b9be 2026-01-12 202: // 6:
d87e80b9be 2026-01-12 203: // - (headers)
d87e80b9be 2026-01-12 204: // - (mail text)
d87e80b9be 2026-01-12 205: // - 6: </pre>
d87e80b9be 2026-01-12 206: if text.len() < 4096 - ( reply.len() + 6 ) {
1c10bccb4e 2026-01-18 207: body = text.to_string();
f5ed284f8c 2025-06-21 208: text_num = 1;
f5ed284f8c 2025-06-21 209: }
f5ed284f8c 2025-06-21 210: };
1c10bccb4e 2026-01-18 211: let msg = format!("{}{}</pre>", reply, body);
f5ed284f8c 2025-06-21 212:
f5ed284f8c 2025-06-21 213: // and let's collect all other attachment parts
f5ed284f8c 2025-06-21 214: let mut files_to_send = vec![];
f5ed284f8c 2025-06-21 215: /*
f5ed284f8c 2025-06-21 216: * let's just skip html parts for now, they just duplicate text?
f5ed284f8c 2025-06-21 217: while html_num < html_parts {
a044f68fa7 2025-08-23 218: files_to_send.push(mail.html_part(html_num).stack()?);
f5ed284f8c 2025-06-21 219: html_num += 1;
f5ed284f8c 2025-06-21 220: }
f5ed284f8c 2025-06-21 221: */
f5ed284f8c 2025-06-21 222: while text_num < text_parts {
a044f68fa7 2025-08-23 223: files_to_send.push(mail.text_part(text_num.try_into().stack()?)
f5ed284f8c 2025-06-21 224: .context("Failed to get text part from message.")?);
f5ed284f8c 2025-06-21 225: text_num += 1;
f5ed284f8c 2025-06-21 226: }
f5ed284f8c 2025-06-21 227: while file_num < attachments {
a044f68fa7 2025-08-23 228: files_to_send.push(mail.attachment(file_num.try_into().stack()?)
f5ed284f8c 2025-06-21 229: .context("Failed to get file part from message.")?);
f5ed284f8c 2025-06-21 230: file_num += 1;
f5ed284f8c 2025-06-21 231: }
f5ed284f8c 2025-06-21 232:
f5ed284f8c 2025-06-21 233: for chat in rcpt {
f5ed284f8c 2025-06-21 234: if !files_to_send.is_empty() {
f5ed284f8c 2025-06-21 235: let mut files = vec![];
f5ed284f8c 2025-06-21 236: // let mut first_one = true;
f5ed284f8c 2025-06-21 237: for chunk in &files_to_send {
f5ed284f8c 2025-06-21 238: let data: Vec<u8> = chunk.contents().to_vec();
f5ed284f8c 2025-06-21 239: let mut filename: Option<String> = None;
f5ed284f8c 2025-06-21 240: for header in chunk.headers() {
f5ed284f8c 2025-06-21 241: if header.name() == "Content-Type" {
f5ed284f8c 2025-06-21 242: match header.value() {
f5ed284f8c 2025-06-21 243: mail_parser::HeaderValue::ContentType(contenttype) => {
f5ed284f8c 2025-06-21 244: if let Some(fname) = contenttype.attribute("name") {
f5ed284f8c 2025-06-21 245: filename = Some(fname.to_owned());
f5ed284f8c 2025-06-21 246: }
f5ed284f8c 2025-06-21 247: },
f5ed284f8c 2025-06-21 248: _ => {
f5ed284f8c 2025-06-21 249: self.tg.debug("Attachment has bad ContentType header.").await?;
f5ed284f8c 2025-06-21 250: },
f5ed284f8c 2025-06-21 251: };
f5ed284f8c 2025-06-21 252: };
f5ed284f8c 2025-06-21 253: };
f5ed284f8c 2025-06-21 254: let filename = if let Some(fname) = filename {
f5ed284f8c 2025-06-21 255: fname
f5ed284f8c 2025-06-21 256: } else {
f5ed284f8c 2025-06-21 257: "Attachment.txt".into()
f5ed284f8c 2025-06-21 258: };
f5ed284f8c 2025-06-21 259: files.push(Attachment {
f5ed284f8c 2025-06-21 260: data: Cursor::new(data),
f5ed284f8c 2025-06-21 261: name: filename,
f5ed284f8c 2025-06-21 262: });
f5ed284f8c 2025-06-21 263: }
f5ed284f8c 2025-06-21 264: self.tg.sendgroup(chat, files, &msg).await?;
f5ed284f8c 2025-06-21 265: } else {
f5ed284f8c 2025-06-21 266: self.tg.send(chat, &msg).await?;
f5ed284f8c 2025-06-21 267: }
f5ed284f8c 2025-06-21 268: }
f5ed284f8c 2025-06-21 269: } else {
f5ed284f8c 2025-06-21 270: bail!("Required headers were not found.");
f5ed284f8c 2025-06-21 271: }
f5ed284f8c 2025-06-21 272: Ok(())
f5ed284f8c 2025-06-21 273: }
f5ed284f8c 2025-06-21 274: }
f5ed284f8c 2025-06-21 275:
78b11b0319 2026-08-01 276: /// SMTP handler implementation for mailin-embedded.
f5ed284f8c 2025-06-21 277: impl mailin_embedded::Handler for MailServer {
f5ed284f8c 2025-06-21 278: /// Just deny login auth
f5ed284f8c 2025-06-21 279: fn auth_login (&mut self, _username: &str, _password: &str) -> Response {
f5ed284f8c 2025-06-21 280: INVALID_CREDENTIALS
f5ed284f8c 2025-06-21 281: }
f5ed284f8c 2025-06-21 282:
f5ed284f8c 2025-06-21 283: /// Just deny plain auth
f5ed284f8c 2025-06-21 284: fn auth_plain (&mut self, _authorization_id: &str, _authentication_id: &str, _password: &str) -> Response {
f5ed284f8c 2025-06-21 285: INVALID_CREDENTIALS
f5ed284f8c 2025-06-21 286: }
f5ed284f8c 2025-06-21 287:
f5ed284f8c 2025-06-21 288: /// Verify whether address is deliverable
f5ed284f8c 2025-06-21 289: fn rcpt (&mut self, to: &str) -> Response {
78b11b0319 2026-08-01 290: if self.get_id(to).is_ok() {
f5ed284f8c 2025-06-21 291: OK
f5ed284f8c 2025-06-21 292: } else {
78b11b0319 2026-08-01 293: NO_MAILBOX
f5ed284f8c 2025-06-21 294: }
f5ed284f8c 2025-06-21 295: }
f5ed284f8c 2025-06-21 296:
f5ed284f8c 2025-06-21 297: /// Save headers we need
f5ed284f8c 2025-06-21 298: fn data_start (&mut self, _domain: &str, from: &str, _is8bit: bool, to: &[String]) -> Response {
f5ed284f8c 2025-06-21 299: self.headers = Some(SomeHeaders{
f5ed284f8c 2025-06-21 300: from: from.to_string(),
f5ed284f8c 2025-06-21 301: to: to.to_vec(),
f5ed284f8c 2025-06-21 302: });
f5ed284f8c 2025-06-21 303: OK
f5ed284f8c 2025-06-21 304: }
f5ed284f8c 2025-06-21 305:
f5ed284f8c 2025-06-21 306: /// Save chunk(?) of data
a044f68fa7 2025-08-23 307: fn data (&mut self, buf: &[u8]) -> std::result::Result<(), Error> {
f5ed284f8c 2025-06-21 308: self.data.append(buf.to_vec().as_mut());
f5ed284f8c 2025-06-21 309: Ok(())
f5ed284f8c 2025-06-21 310: }
f5ed284f8c 2025-06-21 311:
f5ed284f8c 2025-06-21 312: /// Attempt to send email, return temporary error if that fails
f5ed284f8c 2025-06-21 313: fn data_end (&mut self) -> Response {
f5ed284f8c 2025-06-21 314: let mut result = OK;
14ef340959 2026-01-01 315: smol::block_on(Compat::new(async {
f5ed284f8c 2025-06-21 316: // relay mail
f5ed284f8c 2025-06-21 317: if let Err(err) = self.relay_mail().await {
f5ed284f8c 2025-06-21 318: result = INTERNAL_ERROR;
f5ed284f8c 2025-06-21 319: // in case that fails - inform default recipient
1c10bccb4e 2026-01-18 320: if let Err(err) = self.tg.debug(&format!("Sending emails failed:\n{err:}")).await {
f5ed284f8c 2025-06-21 321: // in case that also fails - write some logs and bail
f5ed284f8c 2025-06-21 322: eprintln!("{err:?}");
f5ed284f8c 2025-06-21 323: };
f5ed284f8c 2025-06-21 324: };
14ef340959 2026-01-01 325: }));
f5ed284f8c 2025-06-21 326: // clear - just in case
f5ed284f8c 2025-06-21 327: self.data = vec![];
f5ed284f8c 2025-06-21 328: self.headers = None;
f5ed284f8c 2025-06-21 329: result
f5ed284f8c 2025-06-21 330: }
f5ed284f8c 2025-06-21 331: }