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A double opt-in (aka COI, Confirmed Opt-in) occurs when a user signs up and is sent an email that includes a link to click and confirm the subscription.
By using a double opt-in confirmation method, the chance of spam addresses being signed up is significantly reduced.
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Do you want to remove your IP/domain from one of our blocklists?
Please use our lookup-service and follow the instructions there in order to get that resolved.