Email Deliverability Checklist

The short answer: An email deliverability checklist should run from the bottom up: DNS and infrastructure first, then authentication (SPF, DKIM, DMARC), then reputation and blacklists, then list quality, then content and sending practice. Fixing a later layer while an earlier one is broken wastes time, because a failed SPF record or a blocklist listing overrides every content tweak.

How to Use This Checklist

The order matters. Each layer depends on the one before it: a receiver cannot trust your reputation if it cannot first confirm who you are, and no subject line rescues a listed IP. Work through the master table, then read the notes for any check you fail. Run it before launching a new domain or tool, after any DNS or provider change, and quarterly as routine.

Where a check says "tool", the free tools on this site cover most of the technical layers. The rest need your mail platform or Google and Microsoft's own dashboards.

The Master Checklist

Layer 1: DNS and Infrastructure

Checks 1 to 3

MX records only affect inbound mail, but a wrong MX after a migration often signals other broken DNS. Confirm they match your current provider.

Reverse DNS (PTR) matters most if you send from your own server or a dedicated IP. Many receivers expect the sending IP to have a PTR record, and prefer one that resolves back to the same IP. On shared platforms such as Google Workspace or Microsoft 365 you do not control it, so skip this check.

TLS and MTA-STS. Most modern providers send over TLS by default. MTA-STS protects inbound mail by telling senders to require TLS to your servers, and is a hardening step more than a spam-folder fix. See the MTA-STS generator if you want it.

Layer 2: Authentication

This layer causes most serious deliverability failures, so spend your time here first. SPF, DKIM and DMARC explained covers the concepts in full.

Checks 4 and 5: SPF

A domain may publish only one SPF record. Two v=spf1 records produce a permanent error and SPF fails for everyone. Each include:, a, mx and redirect costs DNS lookups, and the limit is 10 per RFC 7208. A healthy record looks like this:

yourdomain.com. IN TXT "v=spf1 include:_spf.google.com include:sendgrid.net ~all"

If you are near the limit, read SPF too many DNS lookups. For a new tool, see adding third-party senders.

Checks 6 and 7: DKIM

Each service that sends as your domain needs its own DKIM setup, usually two CNAMEs or one TXT record at a selector such as selector1._domainkey.yourdomain.com. Microsoft 365 requires you to enable signing manually per domain. If a result shows dkim=pass but header.d= is the vendor's domain, DKIM passed but does not align with your From address. For failures, see DKIM signature failed.

Checks 8 to 10: DMARC

A starter record:

_dmarc.yourdomain.com. IN TXT "v=DMARC1; p=none; rua=mailto:dmarc@yourdomain.com"

p=none monitors only. It satisfies Google and Yahoo's requirement that bulk senders publish DMARC, but protects nothing. After reading aggregate reports and fixing every legitimate source, move to quarantine and then reject, following the DMARC policy guide. Check 9 is the one people skip: DNS can look perfect while a specific tool fails alignment, so verify from a real message header.

Layer 3: Reputation and Listings

Check 11: Blacklists

Run the blacklist checker before any large send. If something is listed, stop sending, find the cause and follow how to check an email blacklist. Sending while listed can deepen the problem.

Checks 12 and 13: Provider dashboards

Google Postmaster Tools requires you to verify domain ownership with a DNS record. It reports user-reported spam rate and compliance with Gmail's sender requirements. Google's guidance for bulk senders is to stay below 0.10% spam rate and never reach 0.30%. Low volume may produce no data at all, which is normal.

Microsoft SNDS covers IP addresses, so it is useful only if you control the IP. It reports volume, complaint trap hits and a colour status for that IP.

Layer 4: Lists and Recipients

Checks 14 to 16

Reputation is mostly a record of how recipients react. Three habits protect it:

• Prove consent. Keep the signup source and timestamp. Confirmed opt-in also keeps spam-trap addresses out of your list.
• Suppress automatically. Hard bounces and complaints should never receive another message.
• Prune. Contacts who have not engaged in many months drag down engagement and are more likely to have become recycled spam traps. Try a short re-engagement series, then remove non-responders.

Never mail a purchased list. It combines low engagement, high complaints and spam traps in one step.

Layer 5: Content and Sending Practice

Check 17: Unsubscribe

Promotional mail needs a visible unsubscribe link. Gmail and Yahoo also expect one-click unsubscribe headers on bulk mail, and honouring requests within two days. Details are in Google and Yahoo bulk sender requirements, and the bulk sender compliance tool checks your domain against them.

Check 18: Message construction

• Include a text part alongside HTML.
• Make link text match link destinations, and avoid shorteners.
• Do not send one big image with no text.
• Keep a consistent From name and address.

Checks 19 and 20: Ramp and test

A new domain or IP has no reputation, so start small and grow. The warm-up guide has a sample schedule. Before a major campaign, send to seed inboxes at the providers your audience uses, as described in the testing steps below.

If You Fail a Check

Testing Before a Campaign

The checks above confirm your setup. These tests show how mail performs before you send it.

What "Deliverability" Actually Means

Two terms get mixed up:

• Delivery means the receiving server accepted the message. A bounce means it did not.
• Inbox placement means the accepted message landed in the inbox rather than spam, Promotions or quarantine.

A 99% delivery rate can sit alongside a 40% spam-folder rate, because many providers accept first and filter afterwards. This is why bounce reports alone are a poor test. Real testing has to cover authentication, reputation and placement.

Mail-Tester-Style Scoring

Scoring tools give you an address, you send a real message to it, and they return a report. They are the quickest way to catch broken headers, missing plain-text parts, spammy content and DNS mistakes in a single view.

Mail-Tester (mail-tester.com) is the best-known. It gives a score out of 10 and a breakdown covering SpamAssassin results, authentication, blacklist status, content and links. Free use needs no account but is rate-limited, reportedly to around three tests per day at the time of writing, with paid plans for more. Check the site for current limits.

What a mail-tester score cannot do:

• It scores one message sent to one test address. It does not read your domain's long-term reputation.
• It does not test inbox placement at Gmail, Outlook or Yahoo. A 10/10 can still land in spam if your IP has a poor history.
• It runs SpamAssassin-style rules, which are one filter among many. Gmail does not use SpamAssassin.

Treat a mail-tester score as a linting tool for your message and setup. A score below about 8 usually points at something fixable: a missing DKIM signature, no unsubscribe header, broken HTML or an SPF problem.

Checking Real Inbox Placement

Seed-list testing

A seed list is a set of test mailboxes at major providers. You send your campaign to those addresses, and the tool checks whether each copy landed in the inbox, a promotions tab or spam. This is the nearest thing to a measurement of actual filtering.

GlockApps is one commercial option. It provides seed-list inbox placement tests across multiple providers, alongside authentication and blacklist checks. Other platforms in the space offer similar seed-based tests, usually bundled with monitoring. Prices and seed counts change, so check each vendor's current pricing page.

Seed testing has real limits:

• Seed accounts have no engagement history, while real filters weigh recipient behaviour heavily. Results show direction, not exact percentages.
• Seed-list traffic is recognisable. Some providers treat it differently from genuine mail.
• It tests what you send now, not how your list will behave.

Use seed tests to compare, such as before and after changing a sending platform, and to catch large problems like 80% spam placement. Do not chase a tiny percentage change.

Google Postmaster Tools

For Gmail recipients, Google Postmaster Tools is the only first-party data source. Add your sending domain, verify it with a DNS TXT record, and review the dashboards for:

• Spam rate: the share of user-reported spam among mail delivered to the inbox. Google asks bulk senders to stay below 0.10% and never reach 0.30%. See the Google and Yahoo requirements.
• Domain and IP reputation
• Authentication pass rates for SPF, DKIM and DMARC
• Delivery errors and encryption

Postmaster Tools shows data only when you send enough volume to Gmail users. Low-volume senders will often see empty dashboards, which is not a problem in itself. Microsoft offers comparable data for its consumer mail through SNDS and JMRP, and Yahoo has a sender hub with complaint feedback loop enrolment.

How to Read the Results

Content is rarely the root cause once authentication passes. Reputation, complaint rate and engagement dominate. If a new domain or IP is involved, volume ramp is usually the explanation.

Step-by-Step: Test Before a Campaign

Run this in order the day before a large send.

1. Run a DNS audit. Use the free email audit or run the SPF, DKIM and DMARC checkers individually. Fix any failures first.
2. Check blacklists for your sending domain and IP.
3. Send a real test message through your actual platform, using the same template and From address as the campaign, to a Gmail and an Outlook account you control.
4. Read the headers of both copies and confirm spf, dkim and dmarc all pass, using the email header analyzer if you prefer.
5. Check the unsubscribe headers in that message: List-Unsubscribe and List-Unsubscribe-Post: List-Unsubscribe=One-Click.
6. Send to a mail-tester address and fix anything below roughly 8/10.
7. Run a seed-list test if you have access to a tool that offers one, and compare folder placement against your last campaign.
8. Review Postmaster Tools: spam rate under 0.10% and reputation not dropping. If it is, send to your most engaged subscribers first.
9. Clean the list. Remove hard bounces, unsubscribes and long-inactive contacts.
10. Send in stages. Start with a small, engaged segment and watch complaints and bounces for a few hours before the rest.

Frequently Asked Questions

What is the most important item on an email deliverability checklist?

Authentication. If SPF, DKIM and DMARC fail or are misaligned, receivers have no reliable way to trust your mail, and every other improvement has less effect. Verify it from a real message header, not only from DNS.

How often should I run a deliverability check?

Before each large campaign, after any change to DNS, sending tools or mail provider, and at least quarterly. Check dashboards such as Google Postmaster Tools more often if you send at volume.

Is a DMARC record of p=none enough for deliverability?

It meets the minimum for bulk-sender rules and gives you reports, but it does not stop spoofing. Treat it as step one and plan to move to enforcement once your legitimate senders pass.

Do I need a dedicated IP address?

Not usually. Most small senders do better on a well-managed shared IP. A dedicated IP gives you control over your own reputation, but you must build that reputation yourself through warm-up and consistent volume.

My authentication passes but mail still goes to spam. What next?

Look at reputation and list quality: complaint rate, bounce rate, spam traps and engagement. Then check blacklists and test placement across providers.

How do I test email deliverability for free?

Check SPF, DKIM and DMARC with free DNS checkers, run a blacklist check, send a message to Mail-Tester's free tier, and add your domain to Google Postmaster Tools. That covers authentication, reputation and message quality without paying for a seed-list service.

Is a good Mail-Tester score a guarantee of inbox delivery?

No. It scores a single message and your setup, not your sender reputation or engagement. A perfect score is a sign nothing is obviously broken, not a promise of inbox placement.

Next Step

Run the free email audit to check layers 2 and 3 in one pass. If you want the records fixed and verified for you, see our email security setup service.