You can view all opt-outs/unsubscribes by going to Subscribers > View All > + Filter > choose SMS status > Opted Out > Apply. Click Options > Export on the far right to create a downloadable CSV of your opt-outs. Your exported file will be shown at the top right of your account within a few seconds.
To view who has opted out of a specific message, select that message and scroll down to the Message Activity. Select Opt-outs to see who opted out of texts in response to receiving that specific message.
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