Every ESP migration leaves a fingerprint. When a company moves its newsletter from one provider to another, its SPF record changes — one include disappears, another appears — and because SPF lives in public DNS, the aggregate of those changes is a market-share chart nobody can spin. As of the 2026-07-05 snapshot of our daily scan, that chart says something notable: Mailchimp peaked at 5.03% of top-1M SPF domains in November 2022 and has since slid to 3.69%.
The dataset behind this is OpenINTEL's daily DNS measurement of the Tranco top-1M — 192 snapshots from January 2016 through July 2026, covering 623,370 SPF-publishing domains. You can watch the same series move day by day in our daily email infrastructure report.
The shape of the decline
Two things stand out about the Mailchimp curve. First, the timing: the peak lands in November 2022, roughly a year after the Intuit acquisition closed. We will not claim causation from a DNS record — pricing changes, product direction and the broader unbundling of email marketing all overlap in this period — but the directional break is unambiguous in the data. Second, the slope: this is a drift, not a cliff. Losing 1.34 percentage points over roughly three and a half years means customers leaving as contracts and patience expire, not fleeing overnight.
That slow slope matters for interpretation. Sudden crashes in this dataset usually mean a platform-level event — see the MailChannels cliff for the extreme case. Gradual erosion means the product is losing the comparison shop: every month, some fraction of renewals and new projects pick something else.
Where the share went
SPF data cannot follow an individual domain from one provider to the next and call it a "switch" — but it shows precisely who grew while Mailchimp shrank, and the winners fall into three groups.
- The European suite alternative. Brevo (formerly Sendinblue) grew from 0.1% of SPF domains in 2016 to an all-time high of 1.42% today. It occupies the same all-in-one niche as Mailchimp — campaigns, automation, CRM-lite — at a different price point and with an EU-headquartered data story that plays well with GDPR-conscious buyers.
- The lean challenger. MailerSend went from 0.13% in 2017 to its own all-time high of 1.27%. Its growth tracks the broader pattern of teams picking modern, API-first tools with just enough campaign UI on top.
- The pipes. The biggest beneficiary of the suite erosion is the infrastructure layer itself. Amazon SES now leads the entire category at 6.21% of SPF domains — 2.2x its 2022 share. Many ex-suite customers did not choose a new ESP so much as a new campaign tool that happens to send through SES or a similar pipe underneath. We chart that takeover here.
SPF shares sum to more than 100% because multi-ESP setups are the norm: a domain can include Mailchimp for newsletters and SES for transactional at the same time. A falling Mailchimp share therefore means fewer domains authorise it at all — a stronger signal than seat counts or revenue, which bundles can obscure.
What a migration wave means for the migrators
If you are part of this wave — leaving a big suite for a smaller suite or a pipe-plus-tool stack — the deliverability consequences are predictable and mostly self-inflicted:
- You leave a managed pool. Mailchimp's shared infrastructure carries established reputation and aggressive compliance policing. Your new home — especially a raw pipe — expects you to build sender reputation yourself.
- Your authentication changes. New DKIM selectors, new SPF includes, possibly a new sending subdomain. DMARC alignment that worked for years can silently break on day one of the new setup.
- Mailbox providers see a new pattern. Same content, same list, new IPs and new signing domain reads as a new sender. Placement in the first weeks after a migration is genuinely unpredictable — which is why the switch is the single most important moment to measure rather than assume.
The practical move: run an inbox placement test against the major mailbox providers before the migration as a baseline, again on the first sends from the new stack, and then on a schedule until the curves converge. A migration that saves 30% on the invoice and costs 15 points of inbox placement is not a saving.
The bigger lesson: DNS is a leading indicator
Market reports about ESPs lag reality by quarters. SPF records lag it by hours. Mailchimp's November 2022 peak was visible in public DNS long before any earnings commentary or survey caught up — and the same is true of Brevo's and MailerSend's climbs today. If you are choosing an ESP in 2026, the public trajectory of its SPF share is a data point worth checking alongside the feature matrix; we outline the full method in our guide to reading provider health from DNS.