|Makefile||2677||Apr 16 2019|
|README.html||2252||Jul 20 2017|
|README.txt||2290||Jul 20 2017|
|control||206||Mar 28 2018|
|preinst||1636||Mar 28 2018|
This package builder creates a MuntsOS extension package customized for a particular server that has been configured for SMTP relay over SSH. Given a SSH server public key entry from an OpenSSH known_hosts file, the Makefile builds a MuntsOS extension package that will install everything necessary to enable SMTP relay over SSH.
The mail relay server must have a user mailrelay, that is forced to connect to the server's local SMTP server by adding the following to sshd_config:
AllowUsers mailrelay Match User mailrelay AllowTcpForwarding no ForceCommand /usr/bin/nc localhost 25
The mailrelay user on the server must also have the MuntsOS target's root user SSH public key appended to its authorized_keys file.
The package installer appends an entry to /etc/inetd.conf similar to the following:
127.0.0.1:smtp stream tcp nowait root /usr/bin/ssh -q -T email@example.comIt also appends an entry to /root/.ssh/known_hosts similar to the following:
foo.bar.com,188.8.131.52 ecdsa-sha2-nistp256 BLAHBLABLAHBLABLAHBLABLAHBLABLAHBLABLAHBLABLAHBLABLAHBLABLAHBLABLAHBLABLAHBLABLAHBLABLAHBLABLAHBLABLAHBLABLAHBLABLAHBLABLAHBLABLAHBLABLAHBL
When a program on the MuntsOS target connects to the local SMTP service (at localhost:25), inetd runs an openssh command to open a tunnel to the mail relay server's local SMTP service (also localhost:25).
This eliminates the need to run an SMTP agent program (which would be large and complicated) on the MuntsOS target. It also provides an encrypted tunnel to bypass any ISP (Internet Service Provider) restrictions. ISP's often block access to port 25 SMTP servers other than their own, in an attempt to block SPAM senders.
I am available for custom system development (hardware and software) of products based on embedded Linux microcomputers or other processors.