When I send from my outlook.com accounts using K-9 Mail I receive the error below.
Sending using bluemail or Outlook on my PC has no problems.
Delivery has failed to these recipients or groups:
Your message wasn’t delivered because the recipient’s email provider rejected it.
Diagnostic information for administrators:
Generating server: HE1EUR02HT228.mail.protection.outlook.com
Remote Server returned ‘550 5.7.520 Message blocked because it contains content identified as spam. AS(4810)’