Start with registering extension in config.neon:
extensions: mailing: Ublaboo\Mailing\DI\MailingExtension
Now there are several config options:
mailing: do: both # log|send|both log_directory: '%appDir%/../log/mails' # this is default option mail_images_base_path: %wwwDir% # this is default option mails: 
Let's discuss each of these options:
In this option you may choose between these three directives:
- log means all mails will be just stored on local disk in log directory. All mails are saved in .eml format (with possible images and attachments)
- send will only send all mails, but not log
- both will do both
That one is pretty obvious. Directory, where mail files (.eml) will be stored.
This is the path, where Nette\Mail\Message will look for all images that can be inline embedded in mail.
This array filled with your parameters (probably mail addresses - like recipients, senders, etc) will be available in instance of each of your mail class (read more) so that you can easily set sender and recipient, bcc, cc or whatever you need for particular mail.
mailing: mails: [ default_sender: email@example.com ]