How to Test Email Deliverability: A Complete Checklist

You want to know whether your emails will reach inboxes before you send an important campaign, or you have noticed deliverability slipping and want to find out why. Testing deliverability means checking three things: your authentication setup, your reputation, and where your messages actually land.

This guide walks through the full process, from checks you can run in five minutes to the header you need to read when a test message goes to spam.

Test your authentication records

Authentication is the foundation. Start here because authentication failures are the most common cause of spam filtering and the easiest to fix.

SPF

Your SPF record declares which servers may send for your domain. Test your SPF record and confirm:

• A record exists. No record is the first problem.
• Every sender is included. Your mail provider, marketing platform, CRM, helpdesk, and transactional service all need to be listed.
• The syntax is valid. One typo invalidates the whole record.
• You are under the lookup limit. SPF allows ten DNS lookups. Over that, the record fails for everyone.

DKIM

DKIM signs your messages. Test your DKIM record for each service that sends as your domain:

• The DNS record exists at the selector the service uses
• The public key is valid and not truncated
• Signatures verify on a real test message

Every service uses its own selector. If you send through three services, you have three records to check.

DMARC

DMARC ties SPF and DKIM together and tells receivers what to do when they fail. Check your DMARC record and confirm:

• A record exists
• The policy is set. p=none only monitors. p=quarantine or p=reject protect the domain.
• Reporting is on. The rua tag should point at an address that receives aggregate reports.

If you are new to DMARC, start at p=none, use the reports to confirm every legitimate source passes and aligns, then tighten the policy.

MX

MX records handle incoming mail, but they are part of the same infrastructure and often break during DNS migrations. Verify your MX records after any DNS or hosting change.

Test your reputation

Perfect authentication does not stop reputation problems from sending mail to spam.

Blacklists

Run a blacklist check on your sending domain and IP addresses. A listing on Spamhaus, Barracuda, or SpamCop affects delivery immediately. If you find one, the listing page usually explains why. Fix the cause, request removal, and monitor for relisting.

Sending metrics

Your ESP dashboard shows the numbers providers judge you on:

• Bounce rate under 2%. Higher points at list quality.
• Complaint rate under 0.1%. Gmail's hard limit is 0.3%, but you are already being filtered well before that.
• Open and click trends. A decline that is not explained by content or timing usually means placement has shifted.

Google Postmaster Tools shows Gmail's view of your domain, and Microsoft SNDS shows the same for your IPs at Outlook.

Send test emails

Tools tell you what your DNS says. A real message tells you what receivers do with it.

Create test accounts

Set up free mailboxes at Gmail, Outlook.com, Yahoo Mail, and iCloud. If you send to businesses, add a Google Workspace and a Microsoft 365 mailbox too. Between them they represent most of your recipients.

Send representative messages

Send from your production service, not from a personal account. Match the content, length, links, and images of what you really send, and include both transactional and marketing styles if you send both.

Find the spam folder in each mailbox

Knowing where to look saves time when a test message does not appear.

Check Gmail's Promotions and Updates tabs as well. A message there is delivered to the inbox, not filtered as spam. Gmail also deletes spam after 30 days, so check promptly.

Check placement and read the headers

For each test message, note whether it arrived, where it landed, and how long it took. Then open the full headers:

• Gmail: open the message, three-dot menu, "Show original"
• Outlook.com: three-dot menu, "View message source"
• Yahoo: three-dot menu, "View raw message"

The line you want is Authentication-Results.

Worked example: a message that passes everything and still fails DMARC

This is the result that confuses most senders. The test went out through a marketing platform, and Gmail recorded:

Authentication-Results: mx.google.com;
       spf=pass (google.com: domain of [email protected] designates 192.0.2.10 as permitted sender) [email protected];
       dkim=pass [email protected] header.s=default header.b=Xy9zLm2q;
       dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=yourdomain.com

SPF passed. DKIM passed. DMARC failed anyway. Look at the domains:

• SPF passed for mail.esp-example.net, the platform's bounce domain, not yours.
• DKIM passed for esp-example.net, the platform's signing domain, not yours.
• Your From address is yourdomain.com.

DMARC needs at least one of the passing checks to be for your domain. Neither was, so the message is authenticated as the platform's mail, not as yours. This is an alignment failure, and it is the default state of most ESP accounts until you complete "domain authentication" or "custom sending domain" in the platform, which switches both the bounce domain and the DKIM signing domain to yours. See DMARC alignment explained.

If the header instead shows spf=fail or spf=softfail, your SPF record is missing the sending service. If it shows dkim=fail, see DKIM fail. If everything passes and aligns but the message still lands in spam, the cause is reputation, and you should check blacklists and your complaint rate next.

Interpret the rest of the results

Landing in spam with authentication passing

Check blacklist status, then bounce and complaint rates, then engagement history. Content is the last thing to review, and only for the formatting patterns that tip borderline mail: capitals and stacked punctuation in subjects, image-only messages, shortened links, no unsubscribe link.

Landing in Promotions or Updates

Gmail sorts by content type and sender pattern. Marketing content goes to Promotions, notifications to Updates. This is inbox delivery. If you want the Primary tab, send personal, text-first messages, but engagement matters more than the tab.

Different results at different providers

Inbox at Gmail and spam at Outlook usually means a provider-specific reputation issue. Check SNDS for your IPs, look for a listing on a list that Microsoft uses, and compare the headers at each provider.

Set up ongoing monitoring

A test is a snapshot. DNS records get edited, new sending services get added without an SPF update, DKIM keys rotate, blacklist listings appear overnight, and reputation drifts. Monitor authentication records daily, blacklist status regularly, sending metrics after every send, and run a placement test at least monthly. See why set-and-forget authentication is a myth.

The complete checklist

Authentication

• [ ] SPF record exists and is valid
• [ ] All sending services included in SPF
• [ ] Under 10 DNS lookups
• [ ] DKIM record exists for each sending service
• [ ] DKIM signatures verify on a test message
• [ ] DMARC record exists with reporting enabled
• [ ] DMARC policy at quarantine or reject once alignment is confirmed
• [ ] MX records correct

Reputation

• [ ] Not listed on major blacklists
• [ ] Bounce rate under 2%
• [ ] Complaint rate under 0.1%
• [ ] No unexplained drop in engagement
• [ ] Postmaster Tools shows no compliance warnings

Inbox placement

• [ ] Test message reaches the Gmail inbox
• [ ] Test message reaches the Outlook inbox
• [ ] Test message reaches the Yahoo inbox
• [ ] Headers show spf, dkim, and dmarc all passing, with DKIM or SPF aligned to your From domain

Ongoing

• [ ] Monitoring in place for authentication record changes
• [ ] Monitoring in place for blacklist listings
• [ ] A recurring review of sending metrics

Stop Worrying About Email Deliverability

The Email Deliverability Suite monitors your SPF, DKIM, DMARC, MX records and blacklist status daily. Get alerts when something breaks, before your emails stop arriving.