foo@bla:~/Documents/PHP_APPS/PHP_MailApp$ composer require swiftmailer/swiftmailer
Using version ^5.4 for swiftmailer/swiftmailer
./composer.json has been updated
Loading composer repositories with package information
Updating dependencies (including require-dev)
Failed to decode response: zlib_decode(): data error
Retrying with degraded mode, check https://getcomposer.org/doc/articles/troubleshooting.md#degraded-mode for more info
Your configuration does not allow connection to http://packagist.org. See https://getcomposer.org/doc/06-config.md#secure-http for details.
http://packagist.org could not be fully loaded, package information was loaded from the local cache and may be out of date
  - Installing swiftmailer/swiftmailer (v5.4.3)
    Downloading: 50%^C