The share of recipients who opt out of a campaign - the honest verdict on whether your cadence and content are earning their place in the inbox. The benchmark that matters is not sends per week, it is unsubscribes per send: your audience will tell you when you are over-mailing them, one opt-out at a time. The mistake is blasting the list daily with discount codes to hit a send cadence, which trains customers to ignore you or only buy on discount. Restraint is a strategy - fewer, better sends keep open rates high, unsubscribes low and revenue per send strong.
Benchmark. Under 0.3% per campaign means your cadence is healthy. Above 0.5% you are either sending too often or the content is not earning the open. Test your way to the right number, but err on restraint - every email should have a reason to exist.