Email Deliverability

Email deliverability is the rate at which sent emails reach the recipient's inbox versus spam folder or being blocked entirely. It is one of the most important variables in B2B email and one of the most over-engineered topics in vendor pitches.

The four pillars of deliverability

Four factors determine whether an email lands in the inbox.

Authentication. SPF (Sender Policy Framework), DKIM (DomainKeys Identified Mail), and DMARC (Domain-based Message Authentication, Reporting & Conformance) records published in the sender domain's DNS tell receiving mail servers that the email is legitimately from the claimed sender. Without these, modern mail servers (Gmail, Microsoft 365, Yahoo) increasingly route emails to spam or block them entirely.

Sender domain reputation. Mail providers maintain reputation scores for sending domains based on historical behaviour: bounce rate, spam-complaint rate, recipient engagement (opens, clicks, replies), and consistency over time. New domains have neutral reputation and need to be warmed up. Domains with bad reputation get progressively more emails routed to spam.

List quality. A high bounce rate signals to mail providers that the sender is using scraped or stale lists, which degrades reputation. Amazon SES asks senders to keep bounces below 2 percent, reviews accounts at 5 percent and may pause sending at 10. A high spam-complaint rate is even worse: Google asks bulk senders to stay below 0.1 percent. Clean lists with low bounce and low complaint rates are the single most important deliverability lever.

Content. Spam-trigger phrases, ALL CAPS, excessive punctuation, low text-to-image ratios, and shortened URLs all increase spam-scoring. Modern spam filters use ML on patterns rather than keyword blacklists, so the rules are looser than they used to be, but extreme cases still trigger filtering.

SPF, DKIM, DMARC: the authentication trio

SPF tells receivers which IP addresses are allowed to send mail for the sender's domain. The record is a TXT entry in the domain's DNS that lists authorised IPs or includes other authentication services. Missing or misconfigured SPF is a common cause of B2B emails being filtered.

DKIM signs outgoing emails with a cryptographic signature that receivers can verify against a public key published in the sender's DNS. DKIM proves the email was sent from the claimed domain and has not been tampered with in transit.

DMARC ties SPF and DKIM together with a policy: what should the receiving server do if SPF or DKIM authentication fails? Reject, quarantine, or accept-with-report. DMARC also enables aggregate reporting on authentication results.

For B2B sales teams in 2026, all three are essentially mandatory. Sending from a domain without SPF, DKIM, and DMARC properly configured will increasingly result in emails landing in spam or being blocked. Google and Microsoft tightened requirements in 2024.

Sender warm-up

When a sender domain or sending IP is new, mail providers treat it with caution. Sudden high volume from a cold sender is the canonical spam pattern, so unwarmed-up senders typically get most of their early sends routed to spam.

Warm-up is the practice of gradually ramping send volume over weeks to build sender reputation. Modern cold-outreach platforms (Saleshandy, GMass, Snov.io, Lemlist) include warm-up tooling that automates the ramp by having multiple warm-up accounts exchange friendly conversational emails with the sender's address, building positive engagement signals over time.

For B2B sales teams sending one-to-one from their own established business inboxes, warm-up is usually not needed, the inbox is already warm from years of normal use. For teams setting up new sending infrastructure (especially cold-outreach platforms with shared sender pools), warm-up is essential.

What Outsolvi does (and doesn't do) for deliverability

Outsolvi does not send emails from its own servers. Everything you send, automated follow-ups included, goes out from your own Outlook or Gmail account, which means your sender reputation is whatever your own business inbox is, typically already good. Outsolvi tracks what you send and never routes it through a shared sending pool, so other senders cannot drag your reputation down.

This is structurally different from cold-outreach platforms that send through their own infrastructure (Saleshandy, Snov.io) or through warm-up pools (GMass with warm-up enabled). For relationship-selling motion, the "send from your own inbox" approach preserves the existing reputation. For cold-blast motion, dedicated cold-outreach infrastructure with warm-up is the right tool.

What B2B sales teams should monitor

Three deliverability metrics matter:

Bounce rate. Keep it under 2 percent, the level Amazon SES asks of its senders. SES reviews accounts at 5 percent.

Spam-complaint rate. Keep under 0.1 percent. Even small spikes trigger reputation damage quickly.

Reply rate by domain. Drops in reply rate from a specific recipient domain (e.g., suddenly nothing from @microsoft.com) often signal deliverability problems at that domain even before the bounce-rate metric catches up.