9. February 2017

Courier Mail Server stops delivering emails after upgrade to 0.76

It might seem like a minor upgrade to go from version 0.75 to 0.76. In the case of Courier Mail Server, it’s a huge change in the orchestration of services.

Courier Mail Server has a very good modular architecture which allows independent control of each aspect of mail delivery. You can separately restart or change each service like MTA, POP or IMAP. Even encrypted variants of servers are available as separate services. The version 0.76 is pushing it even further in the fashion of micro services.

There is new service ‘courier’ which is responsible for scheduling mail delivery after mail was accepted via SMTP or SMTP-SSL. If you’re not aware of this new service you might wonder why is Courier not logging any activity after accepting email. Just make sure that service is running. You can start it by:

service courier start

After the start of the service, you may see that emails are being processed, but they’re not delivered to local mail users. In the log, you can find many error messages like:

/usr/bin/maildrop: Unable to change to home directory.

The other major change is the switch from courier-maildrop to common maildrop. That might seem like a minor change, but it could render your server completely useless. Emails won’t be simply delivered to user’s mailbox:

/usr/bin/maildrop: Unable to change to home directory.

The problem is that maildrop is accepting different parameters than courier-maildrop. Package maintainers recommends to change line with maildrop in /etc/courier/esmtpd from:



DEFAULTDELIVERY='|/usr/bin/maildrop -w 90 -V 1 -d ""'

If you do not have time to play with maildrop, you can change to default configuration:


Here is the explanation of changes from package maintainers (click image for detail):

Restart services and delivery should start. It might happen that services do not shut down, because upgrade changed user from ‘daemon‘ to ‘courier‘. Then the solution is to terminate services by:

pkill -9 -f courier

Then you can start services and everything should work ok.

1. January 2017

Excellent talks from GOTO Stockholm 2016

I’d like to share with you references to great talks from GOTO Stockholm 2016 related to software development. These speakers are talking about concepts and ideas that are definitely breaking comfort zone of software development.

It is not just Microservices – Fred George

Key takeaway: “If you are doing iteration cycles by two or three weeks and you did it last year or year before. You’re not agile anymore. You should be going faster and faster.”

Software that Fits in Your Head – Dan North

Key takeway: “This is uncomfortable truth. Code is not an asset. Code is the cost.”

26. December 2016

How to build app with MobX annotations via webpack using Babel 6

I was searching for hints how to build games based on React. There is nice simple react-game-kit. The kit contains demo where you can as a player discover the kit itself.

Just type:

git clone git@github.com:FormidableLabs/react-game-kit.git
cd react-game-kit
npm install
npm start

Then you can open the demo in your browser: http://localhost:3000/


I was trying to build my own game based on code from react-game-kit. I hit one problem that webpack was not able to process MobX annotation @observable in GameStore.

Module build failed: SyntaxError: Unexpected token (4:2)

  2 | 
  3 | class GameStore {
> 4 |   @observable characterPosition = { x: 0, y: 0 };
    |   ^

The problem is described in MobX documentation. The annotation @observable is available only in ES7 which is fairly new. In case of Babel 5 or 6 you should use “Stage 0” processing.

Here is how to fix the problem:

npm install babel-plugin-transform-decorators-legacy --save-dev
npm install babel-preset-stage-0 --save-dev

The first package “transform-decorators-legacy” allows you to use decorators with Babel 6. The second package allows you to enable plugins in Stage 0 of build by Babel.

Then you need to tell webpack to use the plugin for decorators transform. Add list of plugins to query section of webpack.config.js:

  query: {
    presets: ['es2015', 'react'],
    plugins: ['transform-decorators-legacy', 'transform-class-properties']

Now you can start the webpack and @observable will be processed.

If you want to learn more about MobX, there is nice tutorial at Egghead.io.

10. February 2016

Story behind PF2016

Slides available in formats: PDFSlideShare

Source code: GitHub/ysoftdevs/pf2016

14. December 2015

Slides from talk at FI MUNI: C++ and Software Engineering 2015

Slides available in formats: PDFSlideShare

Source code: GitHub/ysoftdevs/cpp-examples