What is SmtpTelegramGateway

SmtpTelegramGateway is an SMTP gateway that forwards received emails to specified Telegram chats via your Telegram bot. Runs as a windows service, as a unix daemon or as a standalone application. Fully written in C#.

Setup

1. Edit appsettings.yaml. At least specify a telegram bot token and a chat id.

   # The port that the gateway will listen on to receive SMTP e-mail messages, the default is 25. 
   # No authorization is required when connecting to this port, select Basic Authorizathion if it is required
   SmtpPort: 25
   # Your token for the Telegram bot, get it at https://t.me/BotFather when registering the bot
   TelegramBotToken: SPECIFY THERE TELEGRAM BOT TOKEN
   # Define here a list of email addresses and Telegram chats that will receive emails sent to these addresses.
   # Use an asterisk "*" instead of an email address to send all emails to some Telegram chat
   # If you specify a Telegram user chat, the user must be subscribed to the bot
   # If you specify a Telegram group chat, you may need to add a minus sign prior to the group id, the bot must be added to the group
   # If you specify a Telegram channel chat, you may need to add -100 prior to the channel id, the bot must be added to the channel admins and given the right "Post in the channel"
   # For public channel chat, you can specify the channel public @username instead of the channel id
   Routing:
     - Email: "*"
       TelegramChat: SPECIFY THERE TELEGRAM USERID, GROUPID, CHANNELID OR @USERNAME
     - Email: example@test.com
       TelegramChat: SPECIFY THERE TELEGRAM USERID, GROUPID, CHANNELID OR @USERNAME
   # Logging Level. Set to Debug to see the details of the communication between your mail program and the gateway.
   # Set to Error to see less information
   Logging:
     LogLevel:
       Default: Debug

2. Register and run

   • Run SmtpTelegramGateway.exe as a standalone application
   • Or register the program as a windows service

     sc.exe create "SMTP Telegram Gateway" binpath="C:\Program Files\SmtpTelegramGateway\SmtpTelegramGateway.exe" start=auto obj="NT AUTHORITY\LocalService"

     then start the windows service

     sc.exe start "SMTP Telegram Gateway"

   • Or register the program as a systemd service in unix-like operating systems. Create a configuration file /etc/systemd/system/smtp-telegram-gateway.service looking as follows:

     [Unit]
     Description=SMTP Telegram Gateway
     [Service]
     Type=simple
     ExecStart=/usr/sbin/SmtpTelegramGateway
     [Install]
     WantedBy=multi-user.target

     then say systemd to load the new configuration file

     sudo systemctl daemon-reload

     and run the service

     sudo systemctl start smtp-telegram-gateway.service

3. Send a test email and get it in Telegram. Use localhost as an SMTP server address, 25 as a port and no authentifiacation or, if necessary, select the basic authentication method with a fake username and password.

Other configure options

Apart from configuration via "appsettings.yaml," the program can also be configured using command line parameters:

SmtpTelegramGateway.exe --SmtpPort 25 --TelegramBotToken 111:ABC --Routing:0:Email * --Routing:0:TelegramChat 222 --Logging:LogLevel:Default Debug

or using environment variables:

SmtpPort=25
TelegramBotToken=111__ABC
Routing__0__Email=*
Routing__0__TelegramChat=222
Logging__LogLevel__Default=Debug

or using file appsettings.json:

{
  "SmtpPort": 25,
  "TelegramBotToken": "SPECIFY THERE TELEGRAM BOT TOKEN",
  "Routing": [
    {
      "Email": "*",
      "TelegramChat": "SPECIFY THERE TELEGRAM USERID, GROUPID, CHANNELID OR @USERNAME"
    },
    {
      "Email": "example@test.com",
      "TelegramChat": "SPECIFY THERE TELEGRAM USERID, GROUPID, CHANNELID OR @USERNAME"
    }
  ],
  "Logging": {
    "LogLevel": {
      "Default": "Debug"
    }
  }
}

You can also combine these methods.