nitmo fakeSMTP

Monit, by default, sends out mails to notify about the configured actions. There also is the possibility to execute a script rather than send an email, but there are some limitations in this approach (no reminder for example). So the idea was to build a STMP Server as tiny as possible and to have as little dependencies as possible (ends up in < 2k Byte of code).

The nitmo fakeSMTP is therefore written totally in bash with only using (1) binaries that should be at hand even on an Alpine or any other *nix System (PLEASE file an issue if not).

HANDLE WITH CARE: Its solely purpose is to receive Monit mails! It is not meant to be a SMTP drop-in replacement. It does not even know basic SMTP-Commands (like noop or rst), because Monit doesn't make use of them.

Dependencies

• od
• tr
• sed
• Socket handler (see examples for systemd, inetd/openbsd-inetd, and xinetd in Installation section)

Installation

I assume that nobody who uses monit has to be introduced to using sudo, bash, and a text editor.

• Make the nitmo_fakesmtp.sh executable (chmod +x nitmo_fakesmtp.sh) and remember its path (/usr/local/bin or /usr/local/sbin might be a good place if you do not want to remember the path).
• Make the script listen to a port

  • With systemd (recommended)

    • Copy fakeSMTP.socket and fakeSMTP@.service to /etc/systemd/system
    • Change the ExecStart in fakeSMTP@.service to the correct path of your executable (skip this if the path is inside $PATH)
    • Change the ListenStream in fakeSMTP.socket to the port your want your fakeSMTP to listen to (skip this if port 2525 is okay for you). WARNING: Do not remove the 127.0.0.1 part since the fakeSMTP would then be open to connections from the internet!
    • Enable the socket with systemctl enable fakeSMTP.socket

  • With inetd (not tested, creates open relay if used unaltered!!! )

    • Add the following line to your /etc/inetd.conf:
    • 2525 stream tcp nowait root /path/to/nitmo_fakesmtp.sh
    • Take security steps because inetd cannot (by default) limit connections by itself. See tcpd or similar to protect against installing an open relay!
    • Sharing your installation steps by providing an issue or pull request is greatly appreciated.

  • With xinetd (not tested, creates open relay if used unaltered!!! )

    • Convert the inetd example with xconv.pl (previously itox) that should be provided with xinetd:
    • xconv.pl <<< "2525 stream tcp nowait root /path/to/nitmo_fakesmtp.sh" > monit_fakeSMTP.xinetd
    • Take security steps because this config does not limit connections. See tcpd or similar to protect against installing an open relay!
    • Sharing your installation steps by providing an issue or pull request is greatly appreciated.

Notification examples

The nitmo_fakesmtp.sh includes examples on calling binaries.

• Be aware that the script trims the lines. So any \r|^M will be removed. If you like to forward to email (ie. sendmail) your have to add \r at least to the header lines!
• An example of dropping mails is included
• An example of logging the mails to files is included
• Calling binary telegram-send (see pip, requires Python)
• Calling a php script (might require php... ;-))
• An example of connecting to slack: https://peteris.rocks/blog/monit-configuration-with-slack/