If you're seeing this error (Error From Intersoft: Error Code: E1437 Description: The contact email address is not a valid email address) when trying to create a shipment with Royal Mail (Intersoft) then this would be due to an entry in your Warehouse settings where the Contact Email Address is either empty or is not valid.
To fix this, please follow the steps below:
Click Warehouse then Manage Warehouses.
Find the Warehouse that the order is coming from and click Edit.
You will see the Contact Email Address field is either empty or has invalid characters in.
Update the Contact Email Address and press Save.
Finally, retry generating the shipment.
If you're still having issues after having followed this, please raise a new case online and reference the title of this article.