Smtp via 0ffice365.com

Extra instelling
Send from is nu ook noodzakelijk en smtp Auth protocol moet aan staan.

Enable SMTP AUTH for specific mailboxes The per-mailbox setting to enable (or disable) SMTP AUTH is available in the Microsoft 365 admin center or Exchange Online PowerShell.
Use the Microsoft 365 admin center to enable or disable SMTP AUTH on specific mailboxes

1. Open the Microsoft 365 admin center and go to Users > Active users.
2. Select the user, and in the flyout that appears, click Mail.
3. In the Email apps section, click Manage email apps.
4. Verify the Authenticated SMTP setting: unchecked = disabled, checked = enabled.

When you're finished, click Save changes.