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 toolQuery any DNS record type — A, MX, TXT, CNAME, NS, SOA, CAA, PTR, and more — for any domain via DNS-over-HTTPS. TTLs, DNSSEC status, and shareable result links.
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