An unsubscription is a click on your email's unsubscribe link: the contact simply leaves your sendings. A complaint is when the recipient reports your email as spam from their mailbox (Gmail, Outlook, etc.): it sends a negative signal to mailbox providers, which can lower the deliverability of all your campaigns.
Both are stored in your Sarbacane Contacts opt-out lists: unsubscribers in the unsubscribers tab, complaints in the Complaints tab. In both cases, the contact is set aside from your next sendings.
They don't remember signing up.
They find your emails too frequent.
The content seems misleading or of no interest.
They can't find the unsubscribe link.
They don't recognize the sender.
Best practice: to receive fewer complaints, offer a clear sign-up, turn on double opt-in on your forms, keep to the frequency announced at sign-up and show a clearly visible unsubscribe link. A contact who unsubscribes is better than a contact who complains.
