A large newsletter is a marketing activity. It can become an infrastructure event within seconds.
That can sound counterintuitive. Recipients may not have opened the email, nobody may be buying, and nothing on the website may have changed. Yet traffic can rise abruptly because email security services fetch links automatically as soon as a message reaches an inbox.
When machines reach your links first
WooCommerce documented this in its own incident report. After sending a newsletter to about 800,000 recipients, requests rose within minutes from roughly half a million to just over a million. Some visitors briefly received 429 responses; the partial outage lasted around three to four minutes.
The cause was neither a release nor a conventional attack. Security scanners in corporate inboxes fetched links at scale. These requests behave differently from normal visits: they arrive quickly and concurrently, often before a person has seen the email.
For small and mid-sized setups, the lesson is not to add server capacity on speculation. The practical step is to treat a major send as you would any other traffic peak: planned, coordinated, and observable.
Four questions before a major send
1. How will it be sent?
If the email platform supports it, send large lists in batches. For WooCommerce’s next campaign, delivery was spread over several hours and the comparable spike did not occur.
2. Who knows about it?
Marketing, the website owner, and hosting or operations should share a time window for larger sends. This matters especially when a list contains many corporate addresses or a campaign links to a small number of central pages.
3. What will be watched?
Before sending, agree who will watch response times, error rates, 429 and 5xx responses, cache behaviour, and the availability of the key landing pages. An alert is useful only if it arrives in time and someone knows what to do next.
4. What happens if capacity becomes tight?
A short fallback plan belongs in the process: pause the send, reduce the batch size, check the current picture, and confirm responsibilities. That is not a lack of faith in the campaign. It protects both the campaign’s impact and the running website.
Autoscaling is not always fast enough
Autoscaling can handle sustained demand well. A simultaneous scanner fetch from hundreds of thousands of inboxes is not a gradual curve, though. It is a jump. New capacity often takes minutes; the peak can arrive and disappear in seconds.
The most effective lever is therefore often ahead of the infrastructure: stagger the send, prepare the important links and landing pages, and choose the time deliberately.
Marketing and website operations meet here
A newsletter should create attention, not accidentally become a stress test. Treating major sends as coordinated operating events reduces avoidable risk without slowing the campaign down.
If you want to clarify which landing pages are critical before a larger campaign, which signals should be monitored, and how a controlled sending process could work, we can support the technical preparation and coordination.