What is the difference between 'single opt-in' and 'double opt-in'?
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A
Single opt-in uses one form field; double uses two
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B
Single opt-in adds the subscriber immediately; double opt-in requires email confirmation before adding
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C
Single opt-in is for B2B; double opt-in is for B2C
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D
Single opt-in is free; double opt-in costs extra