Most of the mails are getting rejected by recipient?
Am I being identified as spam?
Remote servers are considering my mails as spam?
If you have any of the issue as stated above, I would assume that your messages are being routed through high risk delivery pool of Office365, take a look at the below header value in the mail sent.
SFV:SPM, Means Office365 has considered this specific Outbound Message as Outbound Spam, Hence it is delivering the Messages using High Risk Delivery Pool.
You need to enable, Outbound Spam Preferences, Enable to Copy the suspicious mail.
Submit the copy of the mail to Microsoft Professional & You can also submit through spam submission.
There are few reasons & Solutions I am listing here.
- It should be based on Content
- E-mail contains Malicious attachment
- Right Click on actual Email, Once copied to your address
- Right Click & Click on "View Source" See if there are Unwanted links shows up
- If yes, then you may need to run Virus Cleanup in Client system
- Send a blank mail to see if it occurs
- Send using OWA to see if it occurs