Just in case you’re using Mailgun with Mediawiki…

The docs don’t cover this, but [the steps in this post][link] got it working for me:

1. Install composer `apt-get install composer`
2. Run `composer update` from the `extensions/Mailgun` folder
3. Run `php maintainence/rebuildLocalizationCache.php` from the main mediawiki folder.

Running your own services get you into all sorts of fun trouble like this.

[link]: “Mailgun extension producing PHP Fatal Error about dependency Guzzle6”