In order to use The Email Laundry’s Recipient Verification the setting will also need to be applied to O365.
The Email Laundry will then reject any invalid recipients at the connection level of the Email Security Service.
Login to the O365 Admin Console
Navigate Admin > Admin Centers > Exchange
Under Mail Flow Click Accepted Domains
Select your domain and edit
Set your domain type to Internal Relay
If set to Authoritative – modify and save
Add valid users to O365
**More information can be found here**
Navigate back to Accepted Domains
Set domain type to Authoritative
Contact The Email Laundry Support to enable Recipient Verification