If you want to link to an entity by ID, you could just create a page that takes the Request entity as a parameter for a Data View, and use the Page URL functionality, without resorting to Deeplink.
https://docs.mendix.com/refguide/page-properties#2-3-6-url
If you want to go the Deeplink route, then you can use the Object Attribute to specify which attribute in your entity is the unique ID. You may need to create this if you don’t have one already. You can use an AutoNumber attribute, or use Community Commons to create a GUID using the Random Hash action to do this.
https://docs.mendix.com/appstore/modules/deep-link
Hope this helps.
Hey Robert, one more question.
How do I get the GUID as a placeholder in my email template?
Thanks!