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Adding someone automatically as a subscriber based on a field?

One answer

Similar questions have been asked multiple times here over the years. The advise appears to be that you need to create a participant to do that since it is not a built-in feature.
Comments

Donald, if you answer a question, please use an answer.
I don't want to end up being the admin that changes comments to answers, because they where provided as a comment in the first place.

And I violently agree to Donald's answer. This was even discussed last week a google search for 'subscribe attribute automatic site:jazz.net' should reveal some initial hints.