Confirmed opt-in
A subscription pattern where the user actively clicks a confirmation link after submitting their email — also called double opt-in.
Confirmed opt-in (COI), also called double opt-in (DOI), is a subscription pattern where the user submits their email address on a signup form, then receives a confirmation email and must click a verification link before being added to the list. Single opt-in adds the user immediately on form submit; COI requires the second confirmation step.
COI's benefits are list hygiene and proof of consent. Typo'd addresses and form-spam don't make it onto the list, since they never confirm. For GDPR and CASL compliance, COI provides clear evidence of opt-in, which can be valuable in audit scenarios. The cost is a ~10–25% drop in completed signups compared to single opt-in, since some users never confirm.
For most senders, COI is worth the conversion hit. The remaining list is more engaged, deliverability is better, and you sleep better in regulatory environments. For very high-intent audiences (paid product trials, gated downloads), single opt-in with strong list-hygiene practices can be defensible.