Hi Otto,
Have you signed in to activate Outlook for Mac when you set up this application? If not, you need to sign in first to compose and send Emails. This can be done within Outlook by going to Outlook> Activate…. Then you will be prompted to sign in:
You can use either a work or school account or a free Microsoft account to sign in.
Feel free to update to us for any further help.
Thanks,
Eric Yang
