There are a couple of options depending on how strictly you want this enforced on the site.
1. In the member's profile, they can choose not to receive email.
This will prevent them from receiving most email but will not block them from receiving the member Newsletter or things like confirmation upon event registration or membership renewal.
2. Members always have the option to opt-out of receiving the Newsletter but clicking the 'unsubscribe' link in the Newsletter footer.
3. To completely block a member from receiving emails from the website, you will need to add the member's email to the Email Block module.
Go to Apps>Admin Backend>Email Block and add a record for the member's email.
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