There are two ways to request a Developer Account.
Using a Web form
Visit http://developers.mailup.com/setupen to request a developer account (or http://developers.mailup.com/setup if you prefer for the Italian version for both request page and developer account console).
From within a MailUp admin console
Select "Build your own MailUp application" on the bottom of Settings > Account settings > Developer's corner > Integrations web page
Confirm your request
Once you submit the form, you will receive a confirmation email. Click in the link in the email to confirm the request and activate your MailUp Developer Account.
Get your API keys
Log into your new MailUp developer account to /wiki/spaces/mailupapi/pages/36340583.