Email Deliverability: The Complete 2026 Guide

Email inbox providers — Google, Microsoft, Apple, Yahoo — have fundamentally raised their standards in the last two years. In early 2024, Google and Yahoo jointly announced mandatory requirements for bulk senders: SPF and DKIM authentication are no longer optional, DMARC is required, one-click unsubscribe must be supported, and spam complaint rates must stay below 0.1%.

The underlying reason is aggressive ML-based spam filtering. Modern filters don't just look at the content of an email — they analyse the sending reputation of the IP and domain, the authentication chain, the historical engagement pattern of the recipient with that sender, complaint rates from similar recipients, and dozens of other signals. A technically perfect email sent from a poorly warmed domain to a stale list will still land in spam.

This guide walks through every layer of the deliverability stack, from DNS configuration to list hygiene to engagement recovery.

SPF (Sender Policy Framework) is a DNS TXT record that lists the IP addresses and services authorised to send email from your domain. A correct SPF record for a team using Advanza as their sending platform would look like:

`v=spf1 include:_spf.advanza.io ~all`

The `~all` at the end is a soft fail — messages from unlisted sources will be marked suspicious rather than rejected. Use `-all` (hard fail) once you are confident your SPF record is complete, as it offers stronger protection against spoofing.

DKIM (DomainKeys Identified Mail) adds a cryptographic signature to every email your sending platform dispatches. The signature is verified against a public key you publish in DNS. Advanza generates DKIM keys per sending domain and provides the DNS records to publish. Use 2048-bit keys — 1024-bit is now considered insufficient by modern inbox providers.

DMARC (Domain-based Message Authentication, Reporting & Conformance) is the policy layer on top of SPF and DKIM. It tells inbox providers what to do when authentication fails (none/quarantine/reject) and where to send aggregate reports. A starting DMARC record:

`v=DMARC1; p=none; rua=mailto:dmarc-reports@yourdomain.com`

Start with `p=none` for monitoring. After reviewing reports and confirming alignment, move to `p=quarantine`, then `p=reject`.

Shared IP pools are used by most small-to-mid-volume senders. You share an IP with other customers of the same platform. If the platform maintains its pool well (suppressing bad senders quickly), shared IPs are fine for up to around 200,000 emails/month.

Dedicated IPs are typically considered once you send consistently at higher volumes. The reputation is entirely yours — good and bad. A dedicated IP needs a structured warm-up process: starting at a few hundred emails per day and ramping up over 4–6 weeks while monitoring bounce and complaint rates.

If you are evaluating a platform for dedicated infrastructure, confirm whether dedicated IPs and automated warm-up are available today or still part of an enterprise roadmap conversation.

Authentication gets you past the technical gates. List hygiene determines your reputation.

Hard bounces are permanent delivery failures — the address does not exist or the domain is gone. Every hard bounce should be suppressed immediately and never retried. Advanza suppresses hard bounces automatically at the account level.

Soft bounces are temporary failures — the mailbox is full, the server was temporarily unavailable. After five consecutive soft bounces to the same address over 30 days, treat it as a hard bounce.

Inactive subscribers are the most dangerous. An address that has not opened an email in 12 months is far more likely to be converted to a spam trap than an active address. Spam traps are addresses maintained by inbox providers specifically to identify senders with poor list hygiene — hitting one signals that you're sending without consent or not cleaning your list.

Run a re-engagement campaign to inactive subscribers (no opens in 9+ months) before you send your next major campaign. Offer a clear "stay subscribed" CTA. Anyone who doesn't engage within 30 days should be suppressed.

Purchased lists are never acceptable. Every address on a purchased list has not given consent to receive email from you. The complaint rates will be catastrophic, and the probability of hitting spam traps is very high.

Modern inbox providers — particularly Gmail — personalise inbox placement by user. A subscriber who has previously opened, clicked, and replied to your emails is far more likely to receive your next email in the primary inbox than a subscriber who has ignored the last twenty.

This means your most engaged segment receives your emails most reliably — which is what you want. It also means that sending campaigns to low-engagement lists actively harms your deliverability for your engaged audience, because the signal from the inactive addresses drags down your per-domain reputation.

Segment your campaigns by engagement level. Your most important sends — product announcements, high-value nurtures — should go to engaged segments only. Re-engagement and recovery sequences are then used to revive inactive contacts in isolation.

Advanza's engagement scoring model automatically labels contacts as Active (opened or clicked in 90 days), Warm (91–180 days), Cool (181–365 days), or Dormant (no engagement in 12+ months), and can automatically exclude Dormant contacts from production campaigns.

Set up Google Postmaster Tools (free) and Microsoft SNDS (free) for visibility into how the two largest inbox providers view your sending domain and IPs. These dashboards show your domain reputation (High/Medium/Low/Bad), spam rate, and authentication pass rates.

If you see your domain reputation drop:

1. Immediately pause any campaigns that went to low-engagement segments. 2. Review your complaint sources in DMARC reports — which campaigns and which segments generated complaints? 3. Suppress all contacts who received the problematic campaign and didn't engage. 4. Run a small-volume engagement campaign to your highest-quality segment (recent purchasers, active users) to rebuild positive signals. 5. Gradually resume sends with tighter engagement filters.

Reputation recovery typically takes 4–8 weeks of clean sending. It is much easier to maintain a good reputation than to recover a damaged one.