Definition
What is the fatigue threshold of an email sequence?
The fatigue threshold is the point past which one more message in an email sequence costs more in lost-subscriber value than it brings in sales. It is calculated message by message, by comparing the margin the message produces with the number of unsubscribes it triggers, multiplied by the annual value of a subscriber. It is specific to each business and each sequence. It explains why a six-message sequence can bring in less than a three-message one.
The two effects of one more message
One more message in a sequence produces two opposite effects. It generates sales, which the sending platform measures and displays. It also triggers unsubscribes, which the platform measures too, but never converts into dollars.
An unsubscribe is not a neutral data point. The subscriber who leaves takes their entire annual value with them, that is, the margin they would have brought in over a year. Platform reports show a message's revenue and its unsubscribe rate separately, without ever putting them in the same unit. A team that optimizes on those reports keeps adding messages as long as each one brings in something, and destroys the list while believing it is putting it to work. The fatigue threshold puts both effects in the same unit.
How to calculate it
Three lines per message are enough: the gross margin that message generates, returns deducted; the number of unsubscribes it triggers; the annual value of a subscriber in your business. The message's net revenue is the first line minus the product of the other two. The fatigue threshold is reached when that net revenue drops below zero.
Do the calculation message by message rather than for the whole sequence: it is usually the last message that tips over, and removing it improves the total. Two caveats. Some of those sales would have happened anyway, especially on abandoned carts, where the client often came back on their own. Nor is an unsubscribe always a pure loss: a subscriber who would never have become a client was costing you fees. So treat the result as an order of magnitude for deciding, not as exact accounting.
What pushes the threshold back
The fatigue threshold is not fixed: anything that reduces unsubscribes without reducing sales pushes it back. Five settings contribute.
- An overall cap on messages per person per month, all sequences and newsletters combined: the simplest and most effective measure.
- A priority rule between sequences, otherwise a client who triggers three receives six messages in four days.
- Stopping the sequence at purchase: a cart reminder received after the order destroys trust faster than any badly written message.
- No discount in the first message, which teaches clients to abandon their cart to get one.
- An annual review of every scenario, so that no message still mentions a discontinued product or an expired promotion.
What the law requires of every message
Every message in an automated sequence is a commercial electronic message. The CRTC sets out three requirements for sending one: having obtained consent, providing identification information and including an unsubscribe mechanism, that is, a simple way to opt out. They apply to every message, including the third one in an automatically triggered sequence.
Two practical consequences. The unsubscribe link appears in every message of the sequence, not just in the newsletter. A withdrawal of consent stops all active sequences, not just the next send. That second requirement is the one configurations botch most often: the person unsubscribes, the platform removes them from the main list and the sequence keeps running.
Net revenue of a message = margin of the message - (unsubscribes triggered × annual value of a subscriber)
The fatigue threshold is reached when that net revenue drops below zero. Do the calculation message by message, with gross margin net of returns, your actual unsubscribes and your own subscriber value.
Suppose a fictional online store where a subscriber is worth $21.70 of margin a year. It adds a fourth message to its abandoned-cart sequence. That message brings in $900 of margin and drives away 60 subscribers. The value destroyed is 60 × $21.70, or $1,302. The message's net revenue is therefore about minus $400: it is a net loss, while the platform report shows it as a $900 success. Removing it improves the sequence's total. The amounts are a worked example, to be redone with your subscriber value and your actual rates.
We read an unsubscribe as a quantifiable loss, not as a quality indicator. Before recommending that a message be added to a sequence, we put its revenue and its unsubscribes in the same unit, dollars of margin, with the subscriber value calculated in your business. A vendor who relies on the revenue the platform displays is optimizing one half of the equation.
We separate what is decided on your side from what can be delegated. The message cap, the value of a subscriber and the discounts offered in sequences remain your decisions. The net revenue calculation per message, the priority rule between sequences, the check that an unsubscribe stops everything and the annual review of scenarios can be handed over.
Not to be confused with
- Subscriber value
- Subscriber value is the margin a subscriber brings to your business over a year. It is one of the three inputs of the fatigue threshold calculation, not the threshold itself.
- Deliverability
- Deliverability is the ability of your emails to reach the inbox rather than the junk folder. A worn-out list damages it, but the two are measured separately: the fatigue threshold reads in dollars, deliverability in emails delivered.
- Unsubscribe rate
- The unsubscribe rate is the percentage the platform displays after each send. Without a dollar value, it does not say whether a message is a net loss. The fatigue threshold converts it into lost margin.
Related concepts
- Subscriber value
- Deliverability
- Cart abandonment
- Follow-up window
- Onus of proving consent
- Zero marginal cost content
- Customer lifetime value
Further reading
- Automated email sequences: driving sales without exhausting your list
- Email list value: calculating what a subscriber is worth
- Email marketing: deliverability, segmentation and sequences
- CASL and newsletters: consent, identification and unsubscribing
- Cart abandonment: understanding causes and reducing friction
- Quote requests: how quickly should you call a prospect back?
Related services
Frequently asked questions
How many messages should my sequence have?
The number depends on the fatigue threshold, which is specific to your business and to each sequence. Calculate the net revenue of each message: the margin produced minus the number of unsubscribes multiplied by a subscriber's annual value. It is usually the last message that tips over, and removing it improves the sequence's total.
My platform shows my last message brings in revenue, so why remove it?
Because the platform displays the message's revenue, but never the value of the subscribers it drives away. A message that brings in $900 of margin and drives away 60 subscribers worth $21.70 a year destroys $1,302 of value. The report shows it as a success; the net revenue says it is a loss.
How do I keep a client from receiving too many emails?
With an overall cap, expressed as a number of messages per person per month, all sequences and newsletters combined. Add a priority rule between sequences, otherwise a client who triggers three receives six messages in four days. Also check that every sequence stops at purchase.
