Land in the inbox. A complete deliverability guide.

Email deliverability is whether your email reaches the recipient's inbox rather than the spam folder or being blocked entirely. It's driven by authentication (SPF/DKIM/DMARC), sender reputation, list quality, content and recipient engagement. For cold outreach specifically, it also depends heavily on warmup, domain separation and sending volume.

Since February 2024, Google and Yahoo require bulk senders to authenticate with SPF, DKIM and aligned DMARC, keep spam-complaint rates under 0.1% (and never above 0.3%), and offer one-click unsubscribe on marketing mail. Mail that fails these requirements is filtered to spam or rejected. They apply in practice to any serious sending program, not just high-volume marketers.

Plan 2–4 weeks of gradual warmup for new domains and mailboxes, ramping daily volume slowly rather than spiking. Keep some warmup running even during active campaigns to maintain reputation. If you can't wait, pre-warmed mailboxes arrive with reputation already built and can send the same day.

Around 4–5 mailboxes per domain is a safe distribution, with each mailbox sending a conservative 30–50 cold emails per day. To scale, add more mailboxes and more domains rather than pushing more volume through any single inbox — and use automatic sender rotation so no mailbox is overloaded.

The most common causes, in order: missing or unaligned SPF/DKIM/DMARC; no warmup on a new mailbox; a dirty list with bounces or spam traps; sending from a shared or burnt tracking domain; spammy or identical bulk content; sudden volume spikes; and low engagement. Fix authentication and warmup first — they account for most spam placement.

Yes — they're foundational and now mandatory. SPF authorizes your sending servers, DKIM cryptographically signs your messages, and DMARC sets policy and gives you reporting. All three must be present and aligned with your From domain. Without them, modern providers filter or reject your mail regardless of content quality.

For cold outreach, simple, mostly-text emails perform best and land more reliably. Heavy HTML, image-only bodies and multiple links are more likely to be filtered. Keep formatting light, limit links (ideally to one), and make the message read like a personal note rather than a marketing blast.

If you track opens or clicks, yes. Shared tracking domains carry the reputation of every other sender using them, which is a major hidden cause of spam placement. Provision a tracking subdomain on your own domain over HTTPS — or, for cold campaigns, consider disabling open tracking entirely to remove the tracking pixel as a risk factor.

Keep your bounce rate under 3% and your spam-complaint rate under 0.1%. Crossing 0.3% complaints triggers domain-wide filtering at Google. These are the hard thresholds that decide whether providers trust your next send, so verify lists before every campaign and suppress hard bounces immediately.

Watch a per-mailbox reputation score, monitor 12+ blacklists for listings, and check Google Postmaster Tools for domain and IP reputation, spam rate and authentication results. DitLead's deliverability suite consolidates all of this with auto-throttle that cuts volume before reputation breaks.