Hi Bjorn
The SSL checkbox must NOT be ticked when using the Office 365 / Outlook SMTP credentials.
Please also ensure that the Office 365 / outlook domain used in the SMTP settings matches the domain of email addresses saved against each person record > Sales tab.
The other details Giuseppe gave you are correct:
SMTP adress: smtp.office365.com
Port: 587
user address: postmaster@mydomain.com
password: your Office365 admin password
Best regards,
Hansaworld Support