Deliverability is whether your email reaches the inbox — not whether your ESP “sent” it. During our platform tests we watched how tools expose authentication setup, bounce handling, and reputation signals. This guide explains the mechanics so you can evaluate any ESP honestly.
SPF lists servers allowed to send for your domain. DKIM cryptographically signs messages so receivers can detect tampering. DMARC tells receivers what to do on failures and where to send reports. Missing any of these is the fastest way to land in spam — regardless of how pretty your templates look.
In our lab, platforms that surface DNS records clearly and validate them in-panel reduce setup errors. That is a product quality issue, not a minor UX nicety.
Buying lists, ignoring bounces, and mailing cold scraped addresses destroy reputation. ISPs score your domain and IP history. A smaller engaged list outperforms a huge dead list on open rates and inbox placement.
New domains and new IPs need gradual volume. Sudden spikes look abusive. Keep From names stable, align visible From domains with authenticated domains, and avoid URL shorteners that resemble phishing patterns.
Compare platforms on our 2026 email tool ranking and individual reviews. Methodology: how we test.