It sounds like there might be an issue with the SSL/TLS certificate or protocol that SSRS is using to communicate with Office365's SMTP server. One possible solution is to try updating the SSL/TLS protocol used by SSRS to match the version used by Office365. Here are the steps to do this:
- Open the Report Server Configuration Manager and navigate to the Email Settings tab.
- In the SMTP Server field, enter the SMTP server address provided by Office365.
- Set the SMTP Server Port to 587.
- Set the Authentication Mode to Basic Authentication.
- In the User Name and Password fields, enter the Office365 email address and password.
- Click the Advanced button.
- In the Advanced SMTP Settings dialog box, set the SSL Protocol option to TLS.
- Click OK to close the dialog box.
- Click Apply to save the changes.
- Test the email settings to see if the issue has been resolved.
If this does not resolve the issue, you may need to contact Microsoft support for further assistance with troubleshooting the SSL/TLS communication between SSRS and Office365's SMTP server.