sendmail to telegram bot

Description

Traditionally email has been used in Linux to communication or inform the user about some kind of problems. In the current environment it is rather difficult to set up a good mail server so that outgoing mail does not end up in spam.

This project exists to simplify the notification to the end user. In Linux all programs that want to send an email somewhere always use /usr/sbin/sendmail. This project implements that command and also provides a mail-transport-agent package so that it is possible to send mails manually e.g. with the mailutils or bsd-mailx packages (these require that an MTA is installed, usually Postfix/Exim/Sendmail and so on).

Installation

There are two ways to install it:

1. Recommended

   • go to Releases and download the current tg-sendmail_x.x.x_<arch>.deb for your architecture (amd64, arm64 or armhf)
   • install:

   sudo apt install ./tg-sendmail_x.x.x_amd64.deb

   • optionally (to send mails as user):

    sudo apt install bsd-mailx  # or mailutils

2. Manual

   • clone this repo
   • build and copy files to their destinations:

    make build
    sudo cp sendmail /usr/sbin/sendmail
    sudo cp sendmail.yaml.example /etc/tg-sendmail.yaml  # fill values
    sudo touch /var/log/tg-sendmail.log
    sudo chmod 666 /var/log/tg-sendmail.log

The installed package contains a compiled static binary, so Go is only needed to build it, never on the machine where it is installed.

Build package yourself

git clone https://github.com/conformist-mw/sendmail
cd sendmail
sudo apt install devscripts debhelper dh-exec dh-make golang-go
debuild --no-lintian

Dependencies are vendored, so the build needs no network access. To build for another architecture:

dpkg-buildpackage --host-arch arm64 --build=any -d -us -uc

Development

make test   # run the tests
make lint   # gofmt and go vet

Usage

After installation, you can check how it works for cron tasks, which notify the user by email in case of an error:

• add a knowingly erroneous command to the cron:

* * * * * /usr/bin/non-existent-command

Send emails:

$ echo 'Mail from the server' | mail -s 'Test subject' oleg.smedyuk@gmail.com

Find the chat id to configure:

$ sendmail --get-updates

This asks Telegram for the messages sent to the bot. It fails with a 409 Conflict when a webhook is registered for the same bot (for example when the bot is shared with Home Assistant), because Telegram allows only one of the two at a time. In that case take the chat id from the service that owns the webhook, or from a bot such as @userinfobot.

Send files (see telegram bot api limitations):

$ sendmail --send-file /var/log/tg-sendmail.log