I want to send a single mail to a responsible address when a certain event occur in my extension. I had a look to some API (Email, Mailing, MailingAB) but but none of these seem to be the right one. There is an API or a class I can use to send mails?
You may want to have a look at the extension CiviRules that allows you to configure triggers, conditions, and actions such as sending out an email on a certain event.
Take a look at this extension that Sarah Gladstone wrote. It sounds similar to what you're doing and you might be able to get some example code from it.