Before sending out your email to all of your recipients, sending a test mailing to yourself at different inboxes (i.e. Gmail, Outlook, Yahoo!, etc) is a good idea. This way you can fine tune and check that your final email will be shown properly in the inbox of your recipients.
In MailUp, this page allows you to send a test mailing to the Test group (multiple email addresses). Alternatively, you can also send a quick send to one email address directly in the HTML editor.