How to fix email deliverability in 2026: 13 best practices for sales teams

What is email deliverability and why does it matter for outbound

Email deliverability is the measure of whether your emails actually reach a recipient’s primary inbox, rather than getting filtered into spam or rejected outright. It depends on your domain’s authentication, your sender reputation, and how people engage with what you send. Get it right, and your outreach lands where someone can actually read it.

People often use “delivery rate” and “inbox placement rate” as if they mean the same thing, but they don’t. Delivery rate tells you whether the receiving server accepted your email. Inbox placement rate tells you whether that accepted email actually reached the primary inbox, rather than spam or promotions.

For outbound teams, this distinction decides whether pipeline exists at all. A sharp ICP, clean data, and strong copy mean nothing if the email never gets seen. There’s no error message when this happens, just fewer opens, fewer replies, and an empty calendar.

How to set up SPF, DKIM, and DMARC for your sending domain

Authentication is the foundation everything else depends on. A campaign with sharp copy and genuine engagement still lands in spam if the underlying authentication is broken.

SPF records

SPF (Sender Policy Framework) is a DNS record listing which servers can send email on behalf of your domain. A message arriving from an unlisted IP can get rejected or flagged.

Every service sending on your behalf belongs on that list: your email provider, your outreach platform, your CRM. Keeping the record under 10 DNS lookups matters too, since going over that limit causes the whole record to fail quietly.

DKIM signing

DKIM (DomainKeys Identified Mail) attaches a cryptographic signature to each outgoing message. Receiving servers check that signature against a public key published in your DNS, confirming the message wasn’t altered in transit. Most providers generate this key pair automatically, so your main job is publishing the public key correctly.

DMARC policies

DMARC (Domain-based Message Authentication, Reporting and Conformance) tells receiving servers what to do when SPF or DKIM checks fail. It runs on three settings: p=none (monitor only), p=quarantine (send failures to spam), and p=reject (block them).

A sensible rollout starts at p=none for a few weeks while reports come in and legitimate senders get authorized. From there, moving to quarantine, then reject, feels safer once you’re confident nothing legitimate will get caught.

How to verify your authentication is working

Free tools like MXToolbox or Google Admin Toolbox check these records in seconds. Even a small error, a typo in an SPF include, a mismatched DKIM selector, can break the entire chain. lemlist’s Deliverability Hub runs automatic technical audits on connected mailboxes, flagging authentication problems before they hit a live campaign.

Why you want a separate sending domain for cold outreach

Sending cold email from your main company domain puts your whole organization’s reputation at risk. If outbound gets flagged, that damage can bleed into support replies, invoices, and everyday email from your company.

The fix is fairly simple: set up a secondary domain that resembles your main one (something like tryyourbrand.com) and reserve it for outbound only. In lemlist, you can purchase and configure sending domains directly inside the platform, with authentication set up automatically.

How to warm up new mailboxes before sending campaigns

A brand-new mailbox has no sending history, so providers have no reason to trust it yet. Warm-up builds that trust gradually, through real sending and receiving before any campaign goes live.

1. Start with real conversations at low volume

Before automation enters the picture, genuine emails to colleagues or existing contacts carry real weight. Reply threads and opens from real inboxes signal that this is a legitimate, human-operated mailbox.

2. Use an automated warm-up tool

Automated warm-up tools exchange messages with a network of real inboxes, generating opens and replies at a pace that builds reputation without manual effort. Every lemlist seat includes lemwarm, which runs in the background and can pull emails out of spam if they land there.

3. Ramp your sending volume week by week

New mailboxes tend to handle 5 to 10 emails a day at first, increasing gradually over several weeks. Jumping straight to full campaign volume is one of the fastest ways to trigger spam filters.

Set safe daily sending limits and use inbox rotation

A provider’s published limit isn’t a safe limit for cold outreach. Google Workspace technically allows 2,000 messages a day, but sending anywhere near that from one mailbox would wreck deliverability fast. A more realistic range sits at 20 to 50 emails per mailbox per day, once that mailbox is fully warmed.

Scaling volume safely comes down to using more mailboxes, not pushing harder on one. Four mailboxes sending 100 emails each looks very different to a mail server than one mailbox sending 400, even with matching totals. Inbox rotation spreads campaign sends across multiple mailboxes and domains automatically, and lemlist’s Deliverability Hub handles this rotation while capping volume per inbox.

Verify every email address before you send

Sending to invalid addresses causes hard bounces, and hard bounces damage sender reputation directly. A hard bounce means the address doesn’t exist, while a soft bounce is usually temporary, like a full mailbox.

Email verification checks whether an address exists before anything gets sent to it. Here’s what it typically catches:

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  Hard bounce traps: addresses that have been deleted or deactivated

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  Typos: small formatting errors, like gamil.com instead of gmail.com

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  Catch-all domains: domains that accept all mail but may lack a real inbox behind the address

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  Disposable addresses: temporary inboxes that expire within hours

lemlist’s Email Finder & Verifier checks across multiple data providers and double-verifies each address, so sends go only to contacts that actually exist.

Write emails that pass spam filters and get replies

Content shapes deliverability in two ways. Spam filters scan subject lines, body text, and formatting for red flags, and low engagement teaches providers to deprioritize future emails from the same domain.

Keep formatting plain and links minimal. HTML-heavy emails with images and several tracking links resemble marketing blasts, and filters treat them that way. Emails that land well usually look plain, like something a colleague might send.

Personalize with real context. Dropping a first name into a template isn’t personalization on its own. A reference to a recent LinkedIn post or a hiring pattern gives the email a reason to exist, and lemlist’s AI Agentic Enrichment pulls this context from LinkedIn, company sites, and CRM data automatically.

Test one variable at a time. A/B testing subject lines and copy shows what actually drives replies, rather than what seems likely to. Changing one element across comparable segments, with enough volume, gives a result worth trusting.

Be careful with open tracking and link tracking

Open tracking embeds a small invisible image in each email, and click tracking routes links through a redirect domain. Both can trigger spam filters, particularly when the tracking domain isn’t properly authenticated.

Clean your email list and remove inactive contacts

Inactive contacts quietly work against outbound efforts. Every email sent to someone who never opens or replies teaches providers that these messages aren’t wanted, dragging down engagement across the whole list.

List decay moves fast in outbound, since people change jobs constantly and companies get acquired. Re-verifying old lists before reuse, suppressing bounces after every campaign, and sunsetting unengaged contacts all keep a list in working order.

Monitor your sender reputation and deliverability metrics

A problem that goes unseen rarely gets fixed. Google asks senders to keep spam complaint rates below 0.10%, treating 0.30% or higher as a serious warning sign, which makes weekly tracking worth the habit.

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  Bounce rate: a rising hard bounce rate usually points to list quality slipping

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  Spam complaint rate: the share marking email as spam, ideally well under 0.10%

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  Open and reply rates: falling engagement signals that people don’t want these emails

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  Inbox placement rate: the share of sent email reaching the primary inbox

Google Postmaster Tools and Microsoft SNDS offer domain-level reputation data for free. lemlist’s Deliverability Hub pulls these signals into one dashboard alongside per-mailbox health scores.

How to recover when your emails start hitting spam

Deliverability can break even with good habits in place, a DNS record slips during a migration, a bad list sneaks through, someone disables warm-up. When it happens, acting fast limits the damage.

1. Pause campaigns and diagnose the cause

Pausing all outbound from the affected mailbox or domain comes first. Reviewing authentication records, bounce rates, and inbox placement through a seed list usually reveals where the problem started.

2. Fix what broke

Correcting misconfigured SPF, DKIM, or DMARC records addresses technical causes. Cleaning the list and stripping risky formatting addresses the rest, and checking every angle matters more than stopping at the first fix found.

3. Re-warm gradually

Restarting at very low volume, once the root cause is fixed, lets positive engagement rebuild over time. A warm-up tool speeds this along, though the process realistically takes weeks.

4. Switch to a new sending domain if recovery stalls

When a domain’s reputation stays damaged despite weeks of clean sending, standing up a fresh secondary domain often moves faster than waiting it out. lemlist makes this part straightforward, since a new domain can be purchased and configured directly inside the platform.

How to manage deliverability across your entire outbound operation

Individual fixes only stretch so far once a team runs multiple reps, dozens of mailboxes, and several sending domains at once. One rep with broken authentication, or one mailbox past its limit, can drag down the reputation of the whole sending infrastructure.

What most teams actually want at that point is centralized visibility: one view of every mailbox’s health, built-in safeguards like rotation and volume caps, and alerts that fire before a problem reaches the inbox. lemlist’s Deliverability Hub covers this ground, monitoring connected mailboxes, enforcing safe sending patterns, and pre-checking campaigns with Deliverability Boost before a single email goes out.