Seven free interactive tools to size, set up, and troubleshoot cold email infrastructure. All run in your browser — no signup, no email required, nothing sent to a server unless noted.
Size your cold email operation before you spin up inboxes.
How many inboxes do you need for cold email? Enter audience size or daily target, pick aggressive / normal / safe — get exact inbox, domain, and warmup counts.
Use toolHow many domains do you need? Set daily volume and per-inbox policy — the calculator sizes your domain portfolio and estimates yearly registration cost.
Use toolWeek-by-week ramp schedule for every new inbox — from day 1 to full cold volume. Logistic curve, not linear.
Use toolGenerate and validate the three records every cold email domain needs: SPF, DKIM, DMARC.
Build a correct SPF record from your sending sources (Google Workspace, Microsoft 365, SendGrid, Mailgun, SES, Winnr). Also checks any existing domain's SPF.
Use toolGenerate a 2048-bit RSA keypair in your browser. Public key becomes a DNS TXT record; private key stays local. Uses WebCrypto — keys never touch a server.
Use toolGenerate a DMARC policy with your policy strength, rollout percentage, and reporting addresses. Also validates existing DMARC records against 2026 best practice.
Use toolMake your cold email copy land in inboxes, not spam.
Winnr gives you 50+ fully authenticated inboxes in minutes with automatic SPF, DKIM, DMARC, and built-in warming at $0.60/inbox/month.
Get started free