What is a possible implementation for the "Subscribe" feature?

Question

iOS

Good afternoon!
Please advise how it is possible in 2018 to implement the "Subscribe" function for sending materials to email in a mobile application.
The application does not have authorization and user data.
The customer requested this feature in the application.

Answer 1

You can, for example, when you click "Subscribe" ask for email and add it to the mailing list.