Six numbers that matter
Average ROI per $1 spent on email marketing
Source: DMA / Litmus 2025
Active email users worldwide in 2026
Source: Statista
Average open rate across our test ESPs in Q1 2026
Source: BestSends internal testing
Spam complaint rate that triggers Gmail throttling
Source: Google Postmaster
Median cost per 1,000 emails sent at the 10K-subscriber tier
Source: BestSends ESP pricing audit
Monthly list decay across audited B2B newsletters
Source: BestSends 2026 ESP review cycle
Four findings from our 2026 testing cycle
Apple Mail Privacy Protection has permanently broken open rates as a primary metric
Five years after MPP shipped, the marketers who still optimize against open rate are leaving money on the table. The platforms leading the pack (ActiveCampaign, Klaviyo, Customer.io) all default their dashboards to engagement-weighted metrics now. ESPs still treating "opens" as a first-class metric (Mailchimp, Constant Contact) feel a generation behind.
Free plans got worse — except where they got dramatically better
Mailchimp, Brevo, and AWeber tightened their free plans in 2025–2026. MailerLite, Beehiiv, and Sender expanded theirs. The split is creating two distinct markets: legacy ESPs aggressively pushing paid conversion, and modern challengers using generous free tiers as a long-term acquisition strategy.
Deliverability is the new differentiator
Feature parity is everywhere. What separates the top 5 platforms from the next 15 is what happens after you click send. ActiveCampaign and Kit consistently land 92%+ of mail in the inbox in our seed-list testing. The bottom of the pack lands closer to 78%. That gap is worth more than every fancy automation feature combined.
AI features are mostly noise — except for subject lines and copy generation
Every ESP launched "AI" features in 2024–2025. Almost none changed how marketers actually work. The two exceptions: AI subject-line generation (which lifts open rates 3–8% in our tests) and AI copy first-drafts (which save 40–60% of email writing time even after editing). Skip the rest.