Email Deliverability Testing Checklist: The 12-Point Audit Every DTC Brand Should Run Before Their Next Major Send
By Loyal Send, Editorial Team12 min read
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Your emails are going to spam. Maybe not all of them. Maybe not right now. But if you're not systematically running email deliverability testing before every major campaign, you're leaving revenue on the table, and you might not even know it's happening.
Email isn't just a marketing channel anymore. Industry publications now call it your identity and deliverability infrastructure, meaning your sender reputation, domain health, and inbox placement rates directly affect whether customers even see your messages. One misstep and you're not just missing opens. You're training algorithms to distrust your domain for weeks.
This guide gives you a complete email deliverability checklist, 12 steps, sourced from real industry tools and warnings, built for DTC brands that can't afford to gamble with their best revenue channel.
Why Your Next Major Send Might Already Be DOA
Your email program isn't just a marketing channel anymore.
Email has evolved into what industry publications now call your identity and deliverability infrastructure, and that shift changes everything about how you should be approaching your sends. If your domain reputation takes a hit, it doesn't just affect one campaign. It affects every customer touchpoint going forward.
The infrastructure you can't afford to ignore
Here's the reality: your sender reputation is fragile. One bad send can trash it for weeks, and recovery isn't automatic. You have to actively earn your way back.
That means before any major send, you need proper email deliverability testing in place, not just hoping for the best because you used Klaviyo. Your deliverability stack matters as much as your creative.
What MailGenius is warning DTC brands about
MailGenius has explicitly warned that tougher spam filters ahead of Black Friday could devastate campaigns for marketers who don't prepare. The message is blunt: the inbox is getting harder to reach, and the brands that will suffer are the ones treating email like it's 2019.
Industry professionals consistently point to tools like MailTester.com and GlockApps as reliable options for checking where your emails actually land before you blast them to your list.
If you're not running an inbox placement test before your next big send, you're flying blind. And during major shopping seasons, blind is expensive.
This is exactly why we built a 12-point email deliverability checklist, so you're not leaving your revenue to chance when it matters most.
Now you know what's at stake. Let's talk tools.
Before You Run the Audit: Pick Your Testing Stack
Free tools that actually work
You don't need a massive budget to audit your email deliverability testing process. Start with three free tools:
- MxToolbox, Send a test email to ping@tools.mxtoolbox.com and get a full diagnostic on your sending reputation, DNS records, and potential red flags.
- Mail-tester.com, Paste your email content or headers here to get a spam score before you hit send to your list.
- EasyDMARC, Run a free inbox placement test across Gmail, Outlook, and major providers to see where your emails actually land.
What to use MailTester.com and GlockApps for
These two are worth bookmarking for deeper analysis. MailTester.com and GlockApps are both considered reliable for email deliverability testing by industry professionals (Reddit r/Emailmarketing).
MailTester.com goes beyond the basics, it inspects your headers, checks authentication records, and gives you a letter grade that clients like Klaviyo deliverability teams reference when troubleshooting.
GlockApps works similarly and has become a go-to for campaign-level diagnostics, especially useful if you're testing before a big launch.
MailGenius warned that tougher spam filters ahead of major shopping periods could devastate campaigns for marketers who don't prepare (PRUnderground).
No tool catches everything. Cross-reference results and use your best judgment.
Testing stack assembled. Now let's run the audit, starting with authentication.
Authentication: Points 1-3
Your domain is your sender identity. If it's not properly authenticated, your emails never reach the inbox, no matter how good your subject line is.
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Run this email deliverability checklist section before every major campaign send.
1. SPF: Are you authorized to send from your domain?
SPF (Sender Policy Framework) tells receiving mail servers which servers are allowed to send emails on behalf of your domain.
If you're sending from Shopify, Klaviyo, your ESP, and a support tool, all of them need to be listed in your SPF record.
Missing or broken SPF means emails get rejected outright. Not filtered. Rejected.
How to check: Send a test ping to ping@tools.mxtoolbox.com and review your authentication results.
2. DKIM: Is your email cryptographically signed?
DKIM (DomainKeys Identified Mail) adds a digital signature to your emails. It proves the message wasn't tampered with during transit.
Without DKIM, ESPs like Klaviyo deliverability take a major hit. Spam filters assume unsigned emails are untrusted.
Every sending source needs its own DKIM record published in your DNS settings.
3. DMARC: Do you have a policy protecting your domain?
DMARC (Domain-based Message Authentication, Reporting & Conformance) tells receiving servers what to do when SPF or DKIM fails.
Without it, you're completely unprotected. Spoofers can impersonate your domain, and you won't even know it's happening.
Your DMARC policy should start at "monitor" (p=none) and move to quarantine or reject as you validate your setup.
MailGenius warned that tougher spam filters ahead of major shopping periods could devastate campaigns for marketers who don't prepare (PRUnderground).
This is identity and deliverability infrastructure. Get it wrong, and you're not just landing in spam, you're risking your sender reputation permanently.
Run all three authentication checks through MxToolbox. Then run a free inbox placement test with EasyDMARC to verify Gmail and Outlook placement before your next send.
Authentication verified. Now let's talk about your list.
List Health: Points 4-6
4. When did this list last get cleaned?
Dead weight addresses are dragging your sender reputation into the gutter.
Every hard bounce is a strike against you. ESPs, whether you're running Klaviyo deliverability setups or another platform, track your bounce rates. Hit their threshold and your next campaign lands in spam before it even reaches the inbox.
That's the real cost of neglect. Not just lost revenue. Deliverability death.
You need a cleaning cadence. If you haven't scrubbed your list in 90 days, you're sending emails into the void. Hard bounces older than six months? Gone. Role-based addresses (info@, admin@, hello@)? Gone.
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This is basic hygiene on your email deliverability checklist. Do it before every major send.
5. Are these addresses actually deliverable?
Your list looks clean on the surface. But how many of those addresses will actually land in the inbox?
MailTester.com and GlockApps are considered reliable for email deliverability testing by industry professionals, according to discussions in the email marketing community. Run your list through one of these tools, or a dedicated validation service, before you hit send on anything important.
MailGenius warned that tougher spam filters ahead of high-volume periods could devastate campaigns for marketers who don't prepare. If you're sending without validating first, you're rolling the dice.
An inbox placement test tells you what actually lands. Run it. Fix the issues. Then send.
6. What's your engagement breakdown?
Not all subscribers are equal. Your email deliverability testing isn't complete until you segment by engagement.
- Active users (opened in the last 30 days), send your best offers here.
- Cold users (60-90 days), re-engage or warm them back up.
- Inactive users (90+ days), these are your risk zone. Either run a win-back sequence or suppress them.
Because here's the uncomfortable truth: sending to perpetually inactive addresses trains ESPs to distrust you. Low engagement signals = lower deliverability for everyone on your list.
Suppression lists aren't optional. Honor unsubscribes immediately, not in 48 hours, not when you get around to it. The consequences aren't worth the shortcut.
Your engaged list is your asset. Protect it.
List is clean and segmented. Now let's verify you're actually hitting the inbox.
Inbox Placement: Points 7-9
7. Gmail placement rate
Gmail's filters are particularly strict for bulk senders. One filtering misstep and your carefully crafted campaign lands in spam, or worse, gets silently dropped.
Before you send to your full list, run an inbox placement test with EasyDMARC. It shows you exactly where your emails land across Gmail and Outlook, so you're not guessing.
Don't rely on your open rate as proof of inboxing. Open rates measure engagement after delivery, they tell you nothing about the emails that never arrived in the first place.
8. Outlook and Yahoo placement
Outlook uses different filtering logic than Gmail. What lands perfectly in your Gmail test can get flagged by Microsoft's algorithms without warning.
If you're running your email deliverability testing across multiple platforms, you're catching issues before they tank your deliverability. Your Klaviyo deliverability reputation takes hits every time Outlook filters one of your sends to spam, and Microsoft's machine learning models remember.
Test both. Every time.
9. Spam folder risk assessment
Check your spam score in Mail-tester.com before you hit send. A high spam score indicates content or technical issues that need attention before sending to your full list.
MailGenius warned that tougher spam filters ahead of high-volume periods could devastate campaigns for marketers who don't prepare. Testing tools like MailTester.com are considered reliable for catching these issues in advance. Use them.
Everything's checking out. Now let's make sure your reputation can handle the load.
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Sender Reputation: Points 10-12
Your sender reputation is your email program's backbone. Blow it, and nothing else matters, no automation, no segmentation, no clever copy. Your emails end up in spam, and your revenue follows.
10. Domain and IP reputation check
Your sending IP has a reputation score, check it on Google Postmaster Tools if you're a high-volume sender. This free tool shows you domain-level data: spam rate, authentication results, and delivery errors. If you're seeing a climbing spam rate or failed DKIM/SPF checks, fix those before your next major send.
Run an inbox placement test using a tool like MailTester.com to verify where your emails actually land. MailTester.com and GlockApps are considered reliable for email deliverability testing by industry professionals, use them to catch problems before your subscribers do.
11. Volume and sending frequency patterns
Sudden spikes in volume trigger filters, best practice is to gradually ramp up sending for big campaigns. Going from 5,000 to 50,000 emails overnight screams "spam" to Gmail and Outlook algorithms.
MailGenius warned that tougher spam filters ahead of Black Friday could devastate campaigns for marketers who don't prepare. If you're planning a flash sale or product launch, build your volume over 7-14 days. Let the mailbox providers see consistent, legitimate traffic.
12. Mailbox provider throttling risk
Klaviyo deliverability depends heavily on your sending history and reputation, don't blow it with a rushed campaign. When you trigger throttling, your emails queue and delay, destroying timing-sensitive sends like cart abandoners or flash promos.
Mailbox warming with real traffic is essential, automation can't replicate genuine engagement signals. Inbox providers watch how recipients interact with your emails. Purchases, replies, and forwards tell them you're wanted. Automated seed lists don't count.
Before your next send, hit this email deliverability checklist. Your profit margins will thank you.
Your 12-Point Audit in One Place
Here's your email deliverability testing checklist, run it before every major send:
- SPF, DKIM, and DMARC authentication
- List validation and hygiene
- Engagement segmentation
- Inbox placement test
- Domain and IP reputation check
- Volume ramping strategy
- Gmail placement rate
- Outlook and Yahoo placement
- Spam folder risk assessment
- Domain and IP reputation check (detailed)
- Volume and sending frequency patterns
- Mailbox provider throttling risk
MailGenius warned that tougher spam filters ahead of Black Friday could devastate campaigns for marketers who don't prepare (PRUnderground). Your entire email revenue is on the line.
Bookmark this email deliverability checklist. Run it before every campaign, especially Black Friday, Cyber Monday, and holiday season sends.
The brands that prepare will hit the inbox. The ones that don't will pay Zuckerberg's ad prices instead.
Ready to Fix Your Email Deliverability?
If you've made it this far, you know exactly what's broken in your email program, and you have the checklist to fix it.
But knowing and doing are different things.
That's where we come in. Unlike generalist agencies that do SEO, ads, and social media, Loyal Send does one thing: email deliverability. We run the audits, fix the authentication, clean your lists, and make sure your campaigns actually land in the inbox.
We guarantee results: 90 days or we work for free.
If you're serious about protecting your email revenue, especially heading into holiday season, book a free 15-minute strategy call. We'll show you exactly what's wrong and what it takes to fix it.
No fluff. No retainer traps. Just someone who knows email deliverability testing inside and out, working on your numbers.
Or start with our quick video breakdown of the most common deliverability mistakes DTC brands make, and how to fix them before your next major send.