Hello Daniel, its quite easy. enable the developer mode and go to the general settings, you can find the Outgoing mail servers menu under the Technical - Email menu. You can define your valid email account and then do check the test connection, If the given credentials will be correct, then system will showing the success message, then onwards you can use the mail sending functionalities from different areas not only for sending the invoices.

Hello Daniel, in your settings you're able to edit the mail of your society. Odoo will recupere this last. 

Hope this is helpful.