Ok, it seems that the module and the mail are actually working ok. The problem seems to be that I don't know how to tell Zentyal where to deliver the mail.
I have a domain, "mycompany.com". That domain is setup in Zentyal DNS to point to the Zentyal machine, so that when "mycompany.com" is typed in the browser, the webpage hosted in the Zentyal machine is displayed.
That domain is also used for emails, but they are managed by an external provider. Anytime a message is sent from outside Zentyal to
akhasis@mycompany.com, the mail arrives to my external mail manager. The problem is when the message is originated inside Zentyal.
The e-mail is sent without problems, but it is delivered to the Zentyal machine, instead of the external mail provider. I have tried to set that provider's DNS in the Zentyal Mail Exchanger DNS for the domain, but the messages are still delivered to Zentyal.
How can I get messages to be sent to my e-mail provider?