Recipient-Side Scanners Can Dominate a Launch's First Traffic Wave

# Recipient-Side Scanners Can Dominate a Launch's First Traffic Wave ## Claim Capacity planning for a large simultaneous send (email, push, or similar) must account for automated recipient-side clients — mail-security scanners fetching links before delivery — because they can generate the first, largest traffic spike independent of any human recipient action.  ## Scope & conditions - Applies to sends targeting corporate or enterprise inboxes, where link-scanning mail-security products are common and fetch outbound links automatically at or near delivery time. - The spike is concentrated in time (arriving with the send, not spread across a normal open/click curve), which is what makes it capable of overwhelming a site sized for organic traffic. - Doesn't apply, or applies much less, to sends targeting consumer inboxes without enterprise-grade scanning infrastructure in front of them. ## Evidence A WordPress community panel discusses a WooCommerce email-send incident where "delivering 800,000 emails at once meant that scanners arrived all at once, too" — the resulting traffic spike came from corporate mail-security scanners fetching the linked site at send time, before any human recipient had opened or clicked, and the volume was enough to overwhelm the linked site. ## Links - [[3. Resources/MOCs/DevRel MOC]] — because applies-in; this is a concrete launch-engineering/capacity-planning lesson for any team running large sends to a mixed consumer/enterprise audience ## Tests / falsifiers - Compare traffic timing curves for a large send to a known-consumer audience versus a known-enterprise audience — if the enterprise send shows a sharp arrival-time spike absent from the consumer send, that confirms the scanner mechanism specifically (not just general send-time load). - Check server logs from an incident like this for user-agent strings identifying known mail-security scanning products — direct confirmation would strengthen this from "plausible mechanism" to "verified cause." ## Maintenance - Last tended: 2026-08-16 - Next review: 2026-11-16 ## Source - [[3. Resources/Readwise/Articles/'I Only Do Puns on Porpoise' - This Week in WordPress 382]] — YouTube, This Week in WordPress #382. https://www.youtube.com/watch?v=hwB5jZ1M2WA