Sunday, March 17, 2019

Some improvements on my docker simple SMTP relay

I have not done any improvements to one of my first docker containers, a SMTP relay, despite the fact that it has resulted quite popular on docker hub (a 1M+ downloads to date !!). Lately I have done some work and received some pull requests with some improvements that I want to talk about.

The first feature I want to introduce is the addition of rsyslog to enable logging the container output to stdout and to log to remote logging systems. This means that now you can see the logs of the emails being processed by the container on its standard output with the docker logs command.

Also, for the modification of postfix's config file, now instead of using sed to modify it we use the postconf command so it is safer. There are also some new configuration options:

SMTP_PORT 

Added by PR #4. Adds a new variable to configure the server SMTP port to use.


SMTP_HEADER_TAG

Added by PR #7. This will add a header for tracking messages upstream. Helpful for spam filters. It will appear as:
RelayTag: yourheadertag

in the email headers.


SMTP_NETWORKS
Added by PR #12 . This variable will set postfix parameter mynetworks, allowoing you to add additional, comma seperated, subnets to use the relay. The default value allows the following networks:

'10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16'

The value you set will append the entered values to that list, so no need to re-add them to the variable.

Many thanks to all the authors for them !!