Double opt-in
A signup confirmed by clicking a confirmation link in a verification email sent to the address entered, before any campaign is sent.
Why it matters
A smaller but real list is worth more than a large list full of dead addresses: those dead addresses are what damage your sender reputation and push your entire list into spam.
Single opt-in accepts the address as typed. Double opt-in verifies that it exists and that the person entered it themselves.
It costs some signups — those who never confirm — and in return removes typos, made-up addresses, and malicious signups made with someone else's address.
Under the GDPR, consent is required before emailing private individuals in the EU. Double opt-in is not mandatory, but it is the strongest proof in the event of a compliance check: it timestamps the click, from the address itself.
In Mailcheer, it is always on. A form signup enters a 'Pending' state and there is no way around it: without the confirmation click, the address receives no campaigns. Someone who unsubscribed and returns of their own accord goes through the same confirmation — no one is reactivated without their knowledge.