Can my app(third-party app) acess iMessages for user enhancement purposes?
No. iMessage apps don't have access to the contents of the messages that users send. You can access the URL of the messages that your app sends, but not what the user has typed in the Messages input field.
Would my app be rejected if I integrate something like that?
How would you integrate it? The Messages Framework API does not give you access to iMessage conversation content.
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