Email deliverability is the invisible infrastructure that determines whether your Shopify marketing emails reach inboxes or vanish into spam folders. A store can have perfect email copy, flawless segmentation, and compelling offers — and still generate zero revenue if the emails never reach subscribers.
The numbers quantify the problem: the average e-commerce email sender achieves only 83% inbox placement — meaning 17% of emails land in spam, promotions tabs, or are blocked entirely. For a store sending 50,000 emails per month, that is 8,500 emails that never get seen. At an average revenue of $0.10 per email, that is $850 in monthly revenue disappearing into the void.
Deliverability is not a one-time configuration. It is an ongoing practice that encompasses technical authentication, list hygiene, sending behavior, and content quality. This guide covers every component.
How Does Email Deliverability Actually Work?
When you send an email from your Shopify email platform, it does not go directly to the recipient's inbox. It passes through multiple checkpoints, each of which can reject or deprioritize your message.
| Checkpoint | What It Checks | Failure Consequence |
|---|---|---|
| Sending server | Is the email properly formatted? | Email rejected at source |
| DNS authentication (SPF) | Is this server authorized to send for this domain? | Marked as suspicious or rejected |
| DKIM signature | Was the email tampered with in transit? | Marked as suspicious or spam |
| DMARC policy | What should happen if SPF/DKIM fails? | Rejected or quarantined based on policy |
| IP reputation | Does this sending IP have a history of spam? | Throttled, filtered to spam, or blocked |
| Domain reputation | Does this domain have a history of spam? | Filtered to spam or promotions |
| Content filters | Does the email contain spam-like content? | Filtered to spam |
| Engagement history | Do recipients typically open emails from this sender? | Filtered to primary inbox, promotions, or spam |
| Recipient behavior | Does this specific user want this email? | Inbox, promotions tab, or spam |
Think of it as a gauntlet. Your email must pass every checkpoint to reach the primary inbox. Failing any single one can divert it to spam — and repeated failures compound, making future emails even more likely to be filtered.
How Do You Set Up Email Authentication (SPF, DKIM, DMARC)?
Email authentication is the technical foundation of deliverability. Without it, email providers have no way to verify that your emails are legitimately from your brand, and they default to treating them as suspicious.
SPF (Sender Policy Framework)
What it does: SPF tells receiving email servers which servers are authorized to send email on behalf of your domain. It is a DNS TXT record that lists approved sending IPs and domains.
How to set it up:
- Log into your domain's DNS management (your domain registrar or hosting provider).
- Find or create a TXT record for your root domain.
- Add the SPF include for your email platform. For Klaviyo:
v=spf1 include:_spf.klaviyo.com ~all. For Omnisend:v=spf1 include:spf.omnisend.com ~all. - If you send from multiple platforms (Klaviyo for marketing, Google Workspace for business email), include all of them in a single SPF record:
v=spf1 include:_spf.klaviyo.com include:_spf.google.com ~all. - You can only have ONE SPF record per domain. Multiple SPF records cause authentication failures.
Verification: Use a tool like MXToolbox SPF Lookup to verify your record is correctly configured.
DKIM (DomainKeys Identified Mail)
What it does: DKIM adds a cryptographic signature to every email you send, allowing the receiving server to verify the email was not altered in transit and was sent by an authorized system.
How to set it up:
- In your email platform (Klaviyo, Omnisend, etc.), navigate to Settings > Domain Authentication or Sending Domains.
- The platform will generate DKIM DNS records — typically one or two CNAME records.
- Add these CNAME records to your domain's DNS.
- Wait for DNS propagation (up to 48 hours, though typically 1-4 hours).
- Return to your email platform and verify the records.
Key detail: DKIM keys should be rotated annually. Most email platforms handle this automatically, but verify with your provider.
DMARC (Domain-based Message Authentication, Reporting, and Conformance)
What it does: DMARC tells receiving servers what to do when an email fails SPF and DKIM checks. Without DMARC, the receiving server makes its own decision — which is often unpredictable.
How to set it up:
- Create a TXT record for
_dmarc.yourdomain.com. - Start with a monitoring-only policy:
v=DMARC1; p=none; rua=mailto:dmarc-reports@yourdomain.com. - This policy does not block any emails — it simply sends you reports showing who is sending email on behalf of your domain.
- Monitor reports for 2-4 weeks to ensure all legitimate sending sources are properly authenticated.
- Upgrade to quarantine policy:
v=DMARC1; p=quarantine; rua=mailto:dmarc-reports@yourdomain.com. This sends failing emails to spam. - Eventually upgrade to reject policy:
v=DMARC1; p=reject; rua=mailto:dmarc-reports@yourdomain.com. This blocks failing emails entirely.
Why DMARC matters for Shopify stores: In 2024, Google and Yahoo began requiring DMARC records for bulk email senders (5,000+ emails per day). Without DMARC, your emails are increasingly likely to be rejected or filtered to spam by these major providers, which collectively handle 60%+ of consumer email.
How Do You Maintain List Hygiene?
Authentication gets your emails past technical checkpoints. List hygiene determines whether email providers consider your messages wanted. Sending to invalid, inactive, or uninterested contacts is the fastest way to destroy your sender reputation.
Remove hard bounces immediately. A hard bounce means the email address does not exist. Most email platforms automatically suppress hard bounces, but verify this is happening. If your hard bounce rate exceeds 2% on any single send, pause and clean your list before sending again.
Monitor soft bounces. Soft bounces (full inbox, temporary server issues) are normal in small quantities. But if the same address soft-bounces 3-5 times consecutively, it should be suppressed — it is likely an abandoned mailbox.
Suppress unengaged contacts. Subscribers who have not opened or clicked an email in 90-180 days should be moved to a sunset flow and eventually suppressed. This is painful — removing contacts feels like shrinking your audience. But a smaller, engaged list outperforms a larger, unengaged list every time.
Validate new signups. Email validation services (ZeroBounce, NeverBounce, Kickbox) can verify email addresses at the point of signup, catching typos, disposable addresses, and known spam traps before they enter your list. This costs $0.005-$0.01 per validation and is worth every penny.
Never purchase email lists. Purchased lists contain spam traps (fake addresses created by email providers to catch spammers), invalid addresses, and people who have never consented to hear from you. A single send to a purchased list can permanently damage your domain reputation.
How Do You Warm Up a Sending Domain or IP?
If you are setting up a new email platform, switching providers, or sending from a new domain, you need to warm up your sending infrastructure. Sending a large volume immediately triggers spam filters — email providers do not trust new senders until they prove themselves.
Warm-up schedule for a new sending domain:
| Week | Daily Send Volume | Audience |
|---|---|---|
| Week 1 | 500-1,000 | Most engaged subscribers only (opened in last 30 days) |
| Week 2 | 1,000-3,000 | Engaged subscribers (opened in last 60 days) |
| Week 3 | 3,000-7,000 | Engaged subscribers (opened in last 90 days) |
| Week 4 | 7,000-15,000 | All engaged subscribers |
| Week 5 | 15,000-30,000 | Engaged + moderately engaged |
| Week 6+ | Full volume | Full sending audience (still excluding unengaged) |
Rules during warm-up:
- Send only to your most engaged contacts first. High open rates in early sends build positive reputation.
- Send consistently. Do not send 1,000 one day and 10,000 the next. Gradual, consistent increases.
- Monitor bounce rates and spam complaints closely. If either spikes, slow down.
- Do not send cold campaigns during warm-up. Use automated flows (welcome, cart abandonment) which naturally have high engagement.
- Avoid Monday and Friday sends during warm-up. Tuesday through Thursday sees the best engagement.
What Content Practices Affect Deliverability?
Your email content itself influences whether spam filters flag your messages. Follow these guidelines.
Subject line best practices:
- Avoid ALL CAPS (looks spammy to filters and humans)
- Avoid excessive punctuation (!!!, ???, $$$)
- Avoid known spam trigger words: "free," "act now," "limited time," "click here," "buy now," "no obligation" — while these are not automatic spam triggers, they contribute to a cumulative spam score
- Keep exclamation marks to one per subject line maximum
Body content best practices:
- Maintain a balanced text-to-image ratio. Emails that are entirely images (a common approach for designed promotional emails) are more likely to be filtered. Include at least 300 characters of real text.
- Include a visible, working unsubscribe link. This is legally required and a deliverability signal.
- Include your physical mailing address (CAN-SPAM requirement).
- Avoid link shorteners (bit.ly, etc.) — spam filters flag shortened URLs because they obscure the destination.
- Use your own domain for all links, not your email platform's tracking domain.
HTML best practices:
- Use clean, well-structured HTML. Broken or messy code triggers content filters.
- Avoid embedded forms within emails. They rarely work and trigger spam filters.
- Keep email file size under 100KB. Oversized emails are more likely to be clipped (Gmail clips emails over 102KB) or filtered.
How Do You Monitor and Improve Deliverability?
Deliverability is not a set-and-forget configuration. Monitor these metrics continuously and respond to warning signs quickly.
Key metrics to track:
Inbox placement rate: The percentage of emails reaching the primary inbox (not spam, not promotions). Use tools like GlockApps or Litmus to test inbox placement across providers. Target: 90%+ for primary inbox.
Bounce rate per campaign: Should be under 2%. If it exceeds 3%, investigate immediately — your list has quality issues.
Spam complaint rate: Should be under 0.1% (1 complaint per 1,000 emails). Google's threshold is 0.3% — exceeding this triggers deliverability penalties. Monitor via Google Postmaster Tools (free).
Unsubscribe rate: Should be under 0.5% per send. Higher rates indicate content relevance or frequency problems.
Open rate trends: Watch for sudden drops in open rates across campaigns. A 10%+ drop that is not explained by subject line changes often indicates a deliverability problem — your emails are being filtered before recipients can open them.
Tools for monitoring:
- Google Postmaster Tools (free): Shows your domain reputation, spam rate, and authentication status with Gmail.
- Microsoft SNDS (free): Similar data for Outlook/Hotmail recipients.
- MXToolbox (free and paid): DNS record validation, blacklist monitoring, email header analysis.
- Your email platform's analytics: Bounce rates, complaint rates, and engagement metrics per campaign.
Recovery from deliverability problems: If you detect a reputation issue (spiking spam rates, declining open rates), immediately reduce your sending volume to your most engaged segment only. Run a list hygiene pass to remove invalid and unengaged addresses. Verify all authentication records. Send only high-engagement content (flows, not campaigns) for 2-4 weeks while your reputation recovers. Think of it like credit score repair — consistent good behavior over time rebuilds trust.
Deliverability is the tax you pay for the privilege of reaching someone's inbox. Every shortcut — purchased lists, skipped authentication, ignored bounces, blasting unengaged contacts — extracts a cost that compounds over time. The stores with 95%+ inbox placement are the ones that treat deliverability not as a technical checkbox but as an ongoing discipline woven into every email decision they make.