Complaint rate is the share of delivered messages recipients marked as spam. Mailbox providers use it to decide sender reputation for every message after. Google's sender guidelines ask bulk senders to keep it under 0.1% and never reach 0.3%, as measured in Postmaster Tools.
Category
Deliverability
Also known as
spam complaint rate; spam rate
In practice
A spike usually follows a reactivation send to a segment nobody had mailed in a year. Look at the complaint line before any campaign report, find the send that preceded the spike, and add a warm-up rule for old segments. An easy unsubscribe is the cheapest way to keep complaints down; people mark as spam what they can't leave.
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