What is email deliverability?

Email deliverability is the ability for your emails to successfully reach subscribers' inboxes rather than bouncing or being filtered into spam. It depends on authentication, sender reputation, list quality, content practices, engagement rates, and sending infrastructure working together.

What is the biggest factor affecting deliverability?

Sender reputation is usually the single biggest factor. It is influenced by authentication status, engagement metrics, spam complaint rates, bounce rates, sending consistency, and overall sending practices. A poor reputation makes inbox placement difficult regardless of content quality.

How often should I review deliverability?

Large senders sending millions of emails per month should review key metrics daily. Most businesses should perform a comprehensive deliverability audit at least once per month, with quarterly deep dives into authentication records, suppression lists, and engagement trends.

Can perfect authentication guarantee inbox placement?

No. SPF, DKIM, and DMARC are essential for proving legitimacy, but inbox placement also depends on sender reputation, subscriber engagement, content quality, and recipient behaviour. Authentication gets you in the door, but engagement keeps you there.

Should I remove inactive subscribers?

Yes. Regularly suppressing or re-engaging inactive subscribers is one of the most effective ways to protect sender reputation. Mailbox providers treat low engagement as a signal that recipients do not want your emails. Suppressing disengaged subscribers before they become spam complaints is essential for long-term deliverability.

What is a good spam complaint rate?

Most mailbox providers expect spam complaint rates to remain below 0.1% of emails delivered. Exceeding this threshold can trigger filtering or blocking. Some providers recommend aiming for below 0.05% for optimal inbox placement.

How long does it take to recover from a deliverability problem?

Recovery time depends on the severity of the issue. Minor reputation damage from a single poor campaign may recover within weeks with improved practices. Major problems such as blacklisting or sustained high complaint rates can take months of consistent positive behaviour to overcome.

The Ultimate Email Deliverability Checklist (2026 Edition)

Email deliverability is not one setting that you switch on. It is the result of hundreds of small decisions made across infrastructure, authentication, list management, content, reputation, and ongoing monitoring. One mistake will probably not destroy your deliverability. Twenty small mistakes usually will.

This guide brings together everything you should check before sending campaigns in 2026. Whether you send 500 emails a month or 50 million, this checklist will help you maximise inbox placement. The sections are organised by category so you can work through them systematically or jump to specific areas during routine audits.

To use this checklist effectively, go through each section and confirm every item is passing. Items that need attention should be prioritised based on how directly they affect deliverability. Authentication and infrastructure failures generally pose the highest risk, followed by list quality and engagement issues. Use the copy button at each checklist heading to generate a plain-text version you can paste into your project management tool or share with your team.

Authentication Checklist

Without proper authentication, your emails ask mailbox providers to trust a message that could have been forged. Authentication is the first gate your email must pass through. Emails that fail authentication checks are more likely to be rejected, filtered, or quarantined.

SPF

Sender Policy Framework tells mailbox providers which servers are authorised to send email for your domain.

SPF record exists: Publish a TXT record at your root domain. Without it, receivers have no way to verify your sending servers.
Only one SPF record published: Merge all includes into a single record. Multiple records cause SPF to fail.
SPF includes all legitimate sending services: Add includes for each sending platform. Missing services cause legitimate messages to fail authentication.
No unnecessary includes: Remove includes for decommissioned services. Extra includes increase DNS lookups and expand the attack surface.
Fewer than 10 DNS lookups: The DNS lookup limit of 10 means extra includes cause SPF to fail. Use a subdomain or consolidate includes.
Old ESPs removed: Audit and clean up includes quarterly. Stale includes from former providers waste lookups.
SPF passes consistently: Check SPF results in DMARC reports weekly. Inconsistent results suggest configuration drift.

DKIM

DomainKeys Identified Mail provides a digital signature that verifies the email content has not been tampered with and confirms it genuinely came from your domain.

DKIM enabled: Enable in your sending platform. Without DKIM, you lose a major authentication signal.
2048-bit keys used: Generate 2048-bit keys where supported. 1024-bit keys are weaker and some providers require stronger keys.
Every sending platform signs messages: Configure DKIM on every sending service. Unsigned messages from some platforms look inconsistent to receivers.
Keys rotated periodically: Rotate annually or bi-annually. Key rotation limits exposure if keys are compromised.
Selector names documented: Maintain a DNS record inventory. Lost selector records make rotation impossible.
DKIM alignment passes: Align signing domain with the visible from domain. Misaligned DKIM signatures reduce DMARC effectiveness.

DMARC

DMARC tells mailbox providers how to handle messages that fail SPF or DKIM checks and provides reporting on authentication results.

DMARC policy published: Publish a DNS TXT record starting with p=none. Without DMARC, providers use their own judgement for failures.
Aggregate reporting (rua) enabled: Set the rua tag to receive XML reports. Reports reveal authentication failures you might miss.
Forensic reporting (ruf) configured (optional): Set ruf if you have capacity to process reports. Individual failure details help debug specific issues.
Reports reviewed regularly: Check aggregate reports at least weekly. Reports only help if someone reads them.
Policy progresses toward quarantine or reject: Move to p=quarantine then p=reject over time. p=none gives information but no protection.
Alignment configured correctly: Ensure aspf and adkim match your authentication setup. Alignment connects the signing domain to the visible from address.

Additional Authentication

Several other authentication mechanisms strengthen your technical posture and improve deliverability signals.

Reverse DNS (PTR) configured: Set PTR to match your sending hostname. Many receivers check PTR records for matching hostnames.
HELO or EHLO hostname valid: Use your sending domain as the HELO identity. An invalid or missing hostname can trigger filtering.
TLS enforced: Enable TLS on your mail server. Unencrypted connections are increasingly rejected.
MTA-STS implemented: Publish an MTA-STS policy and TLSRPT record. MTA-STS forces encrypted delivery and prevents downgrade attacks.
ARC configured (if forwarding): Enable ARC if subscribers forward to other providers. ARC preserves authentication results through forwarding.
BIMI configured (where appropriate): Publish a BIMI record with a verified logo. BIMI displays your brand logo in supported inboxes.

Domain Reputation Checklist

Mailbox providers do not just evaluate individual emails. They evaluate the reputation of the domain that sends them. A domain with poor reputation history will struggle to reach the inbox regardless of authentication or content quality.

Sending domain has positive history: Use an established domain and warm new domains gradually. New domains lack reputation and must send slowly to build it.
No recent spam incidents: Investigate and resolve any complaint source. A single spam surge can damage reputation for months.
No blacklist listings: Check blacklists monthly and request removal promptly. Blacklisted domains face widespread blocking.
Domain age is not suspiciously new: Send low volume initially on new domains. Very young domains look like spray-and-pray operations to mailbox providers.
Consistent sending identity: Use the same from name and domain across campaigns. Switching between from addresses confuses reputation tracking.
Brand name matches domain: Keep from name consistent with your sending domain. Mismatches reduce trust signals.
From address remains consistent: Pick one from address and keep it. Frequent from address changes reset recipient recognition.

IP Reputation Checklist

IP reputation works alongside domain reputation. If you use dedicated sending IPs, the following items apply directly. If you use shared IPs provided by your email service provider, your focus shifts to the provider's overall reputation management.

Dedicated IPs

IP warmed correctly: Start at low volume and increase gradually over weeks. Cold IPs have no reputation and may be throttled.
Gradual volume increases: Increase volume by no more than 20 to 30 percent per week. Sudden spikes look like compromised accounts.
Consistent sending schedule: Send at similar times and volumes each day. Predictable sending builds positive reputation.
No sudden volume spikes: Plan large sends with gradual ramp-up. Spikes trigger automated filtering.
Bounce rates monitored: Check bounce rates on every campaign. Rising bounce rates indicate list quality problems.
Complaint rates monitored: Track complaint rates at the campaign level. Complaints directly damage IP reputation.
Reputation checked regularly: Use Google Postmaster Tools and Microsoft SNDS weekly. Proactive monitoring catches problems early.

Shared IPs

ESP has strong reputation: Choose a provider with strict sending policies. Your IP neighbours affect your deliverability.
Provider is trusted: Research provider reputation before committing. Established providers invest in reputation management.
No unusually poor shared performance: Monitor your own metrics independently from the pool. A few bad senders can drag down the entire pool.

Infrastructure Checklist

Your sending infrastructure needs to be reliable, secure, and properly configured. Infrastructure issues often cause deliverability problems that are difficult to diagnose because they appear intermittent or environment-specific.

Custom tracking domain configured: Set up a dedicated tracking subdomain. Using your brand domain improves click reputation.
HTTPS enabled on all links: Ensure all tracked URLs use HTTPS. Most mailbox providers prefer HTTPS links.
SSL certificates valid: Monitor certificate expiry dates. Expired certificates cause link failures.
DNS records documented: Maintain an inventory of all email-related records. Lost DNS records take time to restore.
Sending platform maintained: Keep your ESP or mail server updated. Outdated platforms may use obsolete protocols.
API credentials secured: Rotate API keys regularly and use restricted permissions. Leaked credentials enable list bombing.
Webhooks functioning: Test webhook delivery endpoints weekly. Broken webhooks cause missed bounce and complaint processing.
Bounce processing working: Verify bounce handling flows are operational. Unprocessed bounces accumulate and harm reputation.
Complaint feedback loop active: Register for feedback loops with major providers. Feedback loops give you real-time complaint data.

Subscriber Acquisition Checklist

The quality of your email list directly determines your deliverability ceiling. Lists built through ethical acquisition with clear consent produce engaged subscribers and strong reputation. Lists built through shortcuts produce spam complaints and filtering problems.

Subscribers acquired organically: Focus on value-driven signup incentives. Organic subscribers expect your emails.
Clear consent collected: Use explicit opt-in language on signup forms. Consent proves subscribers wanted your emails.
Signup forms secured: Add CAPTCHA or similar protections. Insecure forms allow bot subscriptions.
Double opt-in considered: Enable double opt-in for highest list quality. Confirmed opt-in filters invalid addresses.
No purchased lists: Never buy or rent email lists. Purchased lists contain unknown and uninterested recipients.
No scraped addresses: Build your list through opt-in only. Scraped addresses have not consented.
No harvested emails: Use legitimate collection methods exclusively. Harvesting violates terms of most ESPs.
Source of every subscriber known: Tag subscribers by acquisition source. Unknown sources make troubleshooting impossible.

List Hygiene Checklist

List hygiene is perhaps the most impactful section of this entire checklist. A clean list protects sender reputation, improves engagement rates, and reduces wasted spend on subscribers who will never convert.

Hard bounces removed immediately: Suppress hard bounces within 24 hours. Hard bounces indicate invalid addresses.
Soft bounces monitored: Suppress after 3 to 5 consecutive soft bounces. Repeated soft bounces suggest address problems.
Repeated soft bounces suppressed: Set a maximum soft bounce threshold. Persistent soft bounces reduce deliverability.
Invalid addresses removed: Run list validation regularly. Invalid addresses waste sending resources.
Role accounts reviewed: Remove or segment role accounts (info@, admin@). Role accounts have low engagement.
Spam traps removed: Identify traps through engagement patterns and remove immediately. Spam traps destroy sender reputation.
Duplicate subscribers merged: Deduplicate before every import. Duplicates inflate list size and skew metrics.
Obvious typos corrected: Validate email syntax on signup. typos@gmil.com is a hard bounce waiting to happen.
Imported lists validated: Validate all imported lists before sending. Unknown-quality imports introduce risk.
Database cleaned regularly: Schedule quarterly full list audits. List quality degrades over time.

Engagement Checklist

Modern mailbox providers weigh engagement heavily when deciding inbox placement. Positive engagement signals such as opens, clicks, and replies tell providers that recipients value your emails. Low engagement suggests the opposite and increases filtering risk.

Open rates monitored: Track opens at the campaign and segment level. Trend changes indicate engagement shifts.
Click rates monitored: Compare click rates across segments. Clicks are stronger signals than opens.
Replies encouraged: Include reply prompts in campaigns. Replies signal high-value engagement.
Conversions tracked: Connect email analytics to your CRM. Conversions prove business value from email.
Inactive subscribers identified: Define inactivity based on your send frequency. Inactive subscribers dilute engagement rates.
Re-engagement campaigns run: Send a 3-email re-engagement sequence. Win-back campaigns recover some subscribers.
Long-term inactive users suppressed: Suppress after 6 months of inactivity. Non-engagers are your biggest reputation risk.
Highly engaged segments rewarded: Send premium content to your best segments. Strong engagement deserves stronger messaging.
Segments based on engagement data: Create engagement tiers in your ESP. One-size-fits-all sending ignores subscriber behaviour.

Sending Behaviour Checklist

Mailbox providers prefer predictable senders. Consistent sending patterns signal legitimate marketing operations, while erratic behaviour suggests compromise or poor list management.

Consistent sending schedule: Send on the same days and times. Regular sending builds predictable reputation.
No massive volume spikes: Ramp large sends gradually. Spikes in volume often trigger automated filters.
Campaign frequency stable: Set a consistent cadence and stick to it. Changing frequency confuses recipient expectations.
List expansion gradual: Limit new subscriber additions per day. Adding many subscribers quickly raises suspicion.
Seasonal increases planned: Plan holiday volume increases in advance. Expected spikes are safer than unexpected ones.
Large sends warmed gradually: Warm new lists or IPs over several weeks. Cold sending at high volume is dangerous.

Content Checklist

Good content cannot fix a poor reputation, but poor content can certainly damage one. What you send and how you write it sends signals to both subscribers and mailbox providers.

Subject Lines

Honest: Match the subject to the email content. Misleading subject lines increase spam complaints.
Relevant: Segment so subject lines match interests. Irrelevant subject lines reduce engagement.
No misleading claims: Avoid exaggeration and false urgency. Overpromising erodes trust over time.
No fake urgency: Use urgency only when genuinely time-limited. Repeated fake urgency trains subscribers to ignore you.
Personal where appropriate: Use personalisation that is genuinely relevant. Personalised subject lines can improve relevance.

Body Content

Valuable to the recipient: Audit content quality regularly. Low-value content drives disengagement.
Mobile friendly: Test on mobile before every send. Most email is read on mobile devices.
Proper HTML structure: Validate HTML before sending. Broken HTML triggers spam filter rules.
Plain text version included: Always include a plain text alternative. Missing plain text is a spam filter signal.
Grammar checked: Run all content through grammar tools. Poor grammar looks unprofessional.
Links tested: Check every link before sending. Broken links frustrate subscribers.
Images compressed: Optimise images to under 100 KB where possible. Large images slow loading times.
Alt text added: Add descriptive alt text to every image. Missing alt text hurts accessibility and engagement.
Dark mode considered: Test in dark mode on major clients. Dark mode can invert colours and hide content.

Images

Optimised file size: Keep images under 100 KB where possible. Large images slow email loading.
Fast loading: Host images on a CDN with fast response times. Slow emails get deleted quickly.
Relevant to content: Use images that support the message. Decorative images add little value.
Alt text included: Write descriptive alt text for every image. Alt text displays when images are blocked.
Not image-only emails: Use a text-to-image ratio of at least 60 to 40. Image-only emails hide content when images are blocked.

HTML and Design Checklist

Technical email design decisions affect how your message renders across clients and whether it triggers spam filters.

Valid HTML: Validate HTML against email standards. Invalid HTML can break rendering and trigger filters.
Inline CSS: Use inline CSS for all styling. Many clients strip embedded stylesheets.
Responsive layout: Include media queries for screen size adaptation. Non-responsive emails are hard to read on mobile.
Accessible markup: Use semantic heading tags and proper alt text. Accessibility improves usability for all subscribers.
Good colour contrast: Test contrast ratios for text and backgrounds. Low contrast is hard to read.
Semantic structure: Use proper heading hierarchy. Screen readers rely on structured content.
Tested across email clients: Preview in Gmail, Outlook, Apple Mail, and Yahoo. Each client renders HTML differently.
Dark mode tested: Check appearance in dark mode on key platforms. Inverted colours can hide content.

Personalisation Checklist

Broken personalisation erodes trust faster than almost any other email mistake. A personalised email that outputs "Hello {{firstname}}" because the merge tag failed signals that you do not pay attention to detail.

Merge tags tested: Send test emails to verify every merge tag. Untested tags may output raw placeholders.
Missing data handled gracefully: Set fallback values for every personalised field. Missing fields produce ugly display.
Dynamic content verified: Preview every dynamic content variation. Conditional content may show wrong variants.
No broken placeholders: Check for unresolved placeholders before sending. Raw merge tags look amateurish.
Every variation previewed: Send seed tests for each audience segment. One broken variation is one too many.

Segmentation Checklist

Sending the same message to your entire list ignores the different needs, interests, and behaviours of your subscribers. Segmentation improves engagement, reduces complaints, and directly supports better deliverability.

Geographic segmentation: Segment by country or region where applicable. Location affects relevance of many offers.
Engagement segmentation: Create separate engagement tiers. Engaged and disengaged subscribers need different messages.
Purchase history: Segment based on purchase categories. Past behaviour predicts future interest.
Lifecycle stage: Create lifecycle-based segments. New subscribers need different content than long-term ones.
Customer status: Separate customers from non-customers. Customers and prospects need different messaging.
Behavioural segmentation: Segment based on opens, clicks, and site visits. Actions speak louder than stated preferences.
Preference centre respected: Honour frequency and topic choices. Ignoring preferences causes complaints.

Compliance Checklist

Email regulations exist in most countries. Compliance failures expose you to legal risk and damage trust with both subscribers and mailbox providers.

Consent recorded: Log consent timestamp, source, and IP. Proof of consent is your best defence.
Unsubscribe link visible: Place unsubscribe in the email footer. Hidden unsubscribe links increase spam complaints.
One-click unsubscribe supported: Implement list-unsubscribe headers. Many providers require one-click opt-out.
Company address included: Add your physical business address to the footer. Required by law in many jurisdictions.
Privacy policy available: Link to your privacy policy in signup forms. Subscribers have a right to know how their data is used.
GDPR requirements met: Review data handling practices annually. GDPR applies to any EU subscriber data.
CAN-SPAM requirements met: Review requirements each year. CAN-SPAM requires honest headers and opt-out.
Local regulations followed: Research applicable regulations for your audience. Many countries have specific email laws.

Monitoring Checklist

You cannot improve what you do not measure. Regular monitoring of key metrics helps you spot problems early and track the impact of improvements.

Delivery rate: Percentage of sent emails accepted by the receiver. Investigate if below 97 percent.
Hard bounce rate: Invalid or non-existent addresses. Investigate if above 2 percent.
Soft bounce rate: Temporary delivery failures. Investigate if above 5 percent.
Inbox placement: How many emails reach the inbox versus spam. Investigate if below 90 percent.
Spam placement: Percentage filtered to spam. Investigate if above 2 percent.
Complaint rate: Subscribers marking your email as spam. Investigate if above 0.1 percent.
Open rate: Subscribers who opened the email. Monitor trend direction over time.
Click rate: Subscribers who clicked a link. Compare to your historical baseline.
Click-to-open rate: Content quality measurement. Investigate if below 10 percent.
Unsubscribe rate: Subscribers leaving your list. Investigate if above 0.5 percent per campaign.
Conversion rate: Subscribers who completed the goal. Compare to your historical baseline.

Reputation Monitoring Checklist

External monitoring tools give you visibility into how mailbox providers view your sending reputation. Review these regularly to catch problems before they affect campaign performance.

Google Postmaster Tools: Check domain reputation, IP reputation, delivery errors, and spam rate. Review weekly, or daily for high-volume senders.
Microsoft SNDS: Check IP reputation, complaint data, and filtered volume. Review weekly.
DMARC aggregate reports: Check authentication pass and fail data by source. Review weekly.
Blocklist monitors: Check listing status on major DNS blocklists. Review weekly.
Sender reputation services: Check composite reputation scores from third-party tools. Review monthly.
Domain reputation tools: Check domain-specific reputation within mailbox ecosystems. Review monthly.
IP reputation tools: Check IP-specific reputation scores. Review monthly.

Automation Checklist

Automated email sequences handle large volumes of email with minimal oversight. This makes them both powerful and risky. An automation that breaks silently can damage your reputation before anyone notices.

Welcome emails tested: Send test versions of every welcome email. Welcome sequences set the tone for subscriber relationships.
Abandoned cart emails tested: Verify cart abandonment fires correctly. Cart triggers depend on correct tracking implementation.
Transactional emails authenticated: Configure SPF, DKIM, and DMARC for transactional streams. Transactional emails bypass some filters when authenticated.
Trigger logic verified: Test every automation trigger condition. Wrong triggers send emails to the wrong people.
Frequency limits enforced: Set maximum send frequency per subscriber. Too many emails cause unsubscribes and complaints.
Duplicate sends prevented: Implement delivery deduplication. Duplicate emails frustrate subscribers and waste sends.

Testing Checklist

Before every major campaign, run through these checks to catch rendering issues, broken elements, and personalisation mistakes before they reach your subscribers.

Desktop preview: Check layout, font sizes, image alignment, and whitespace.
Mobile preview: Check responsive scaling, tap targets, and font readability.
Gmail render: Check for clipping, CSS support, and inbox filtering behaviour.
Outlook render: Check table rendering, background colours, and font fallbacks.
Apple Mail render: Check dark mode, image rendering, and typography.
Yahoo render: Check CSS support and image blocking behaviour.
Dark mode appearance: Check logo visibility, text contrast, and button readability.
All links working: Verify correct URLs, tracking parameters, and destination pages.
All images loading: Verify image hosting, file paths, and alt text fallbacks.
Personalisation rendering: Verify merge tags, conditional content, and fallback values.
Seed test delivery: Confirm reachability across major providers.

Deliverability Warning Signs

These warning signs indicate that something is going wrong. If you notice any of them, investigate the cause immediately rather than continuing to send as normal.

Open rates suddenly halve: Likely cause is inbox placement dropping or list quality deteriorating. Check Postmaster Tools and blacklists immediately.
Spam complaints increase: Likely cause is content mismatch or disengaged subscribers. Pause sends and review recent complaint sources.
Bounce rates rise: Likely cause is list hygiene degradation or a purchased list. Check suppression lists and recent subscriber sources.
Gmail promotions tab emails moving to spam: Likely cause is reputation decline with Gmail. Review Postmaster Tools, authentication, and complaint rates.
Microsoft inbox placement drops: Likely cause is reputation decline with Microsoft. Check SNDS data for feedback and complaint rates.
Authentication failure rate rising: Likely cause is DNS changes or platform configuration drift. Review DMARC reports for failing sources.
Blocklist appearance: Likely cause is a serious reputation issue. Request removal and fix root cause before resending.
Sudden unsubscribe spike: Likely cause is content or frequency mismatch. Review recent campaigns for subscriber-offending content.
Engagement collapsing: Likely cause is list fatigue or poor targeting. Increase segmentation and reduce send frequency.
Major volume changes without warming: Likely cause is infrastructure needing adjustment. Warm new volume levels gradually.

Monthly Deliverability Audit

Once a month, go through these questions to assess the health of your email program. If you answer no to several of them, schedule a full deliverability review before your next major campaign.

Are all authentication records still current and correct? Verify SPF, DKIM, and DMARC records have not drifted.
Has any email service provider changed their sending infrastructure? Check for infrastructure changes that affect configuration.
Have any new sending domains been added without proper configuration? Ensure new domains are authenticated and warmed.
Is sender reputation stable or improving? Review Postmaster Tools and SNDS trends.
Are bounce rates at normal levels? Compare to your baseline thresholds.
Are complaint rates within acceptable thresholds? Keep below 0.1 percent.
Is the inactive subscriber segment growing? Schedule list hygiene if inactivity increases.
Are suppression lists being maintained and applied correctly? Test that bounces and unsubscribes are processed.
Are automated sequences behaving as expected? Review trigger logs for automation errors.
Have any integrations broken since the last audit? Check webhook delivery and API connections.
Are campaigns still reaching inboxes consistently? Verify inbox placement rates.
Is overall engagement improving or declining? Review open, click, and conversion trends.

Deliverability Scorecard

How many items in this checklist did you pass? Use this scorecard to assess your overall deliverability health.

Score Range	Meaning
95 to 100 percent	Excellent. You are following modern deliverability best practices across all categories.
80 to 94 percent	Strong overall, but there are specific improvements worth making. Focus on the items you missed.
60 to 79 percent	Moderate risk. Several areas need attention. Prioritise authentication, list hygiene, and engagement.
Below 60 percent	Your inbox placement is likely suffering. Stop sending and fix the biggest gaps first.

Remember that deliverability is not something you finish. Mailbox providers constantly adjust their filtering systems, subscriber behaviour changes over time, and your sending reputation evolves with every campaign. The best senders consistently maintain good practices across authentication, infrastructure, engagement, content, and list hygiene. They do not obsess over one magic metric.

Think of this checklist as preventative maintenance. Spending an hour reviewing it each month is far easier than spending weeks trying to recover from poor inbox placement.