Email deliverability is how successfully your emails reach subscribers' inboxes (not spam). High deliverability = better open rates, more clicks, higher revenue.
In this guide, you’ll learn the most important deliverability practices to monitor, from technical setup to best practices.
Why Deliverability Matters
Omnisend makes sending emails simple: add your sender domain and email address, upload Contacts, design the email, and hit send.
However, a “Delivered” status doesn’t guarantee your email reaches the inbox. Inbox providers like Gmail, Yahoo, and Outlook use filtering systems to decide whether messages appear in the inbox or the spam folder. If your emails are filtered to spam, subscribers won’t see them, resulting in lower open rates, fewer clicks, and lost revenue.
Monitoring deliverability helps protect your revenue, sender reputation, and customer relationships. Small warning signs, such as increasing spam complaints or declining engagement, can quickly become serious problems if left unaddressed, potentially leading to inbox blocking or account suspension.
Technical Setup for Email Deliverability
Sender Email Address
To create an Omnisend account, you need to provide an email address. This address is used for communication between you and Omnisend. However, to send Email Campaigns or Automation messages, you must add and verify a sender email address. This is the email address your customers see in the From field of your emails.
For best deliverability, your sender email address should use your store’s domain so it matches your brand and is recognizable to both inbox providers and customers (for example, [email protected]).
Prohibited domains for sending emails to real recipients include:
@yahoo.com;
@msn.com;
@hotmail.com;
@outlook.com;
@live.com;
@gmail.com, etc.
💬 Learn how to Set Up Your Omnisend Sender Email Address.
Sender Domain
Your sender domain is your business's web address, the domain used to send your emails (for example, yourstore.com). When you sign your domain in Omnisend, authentication records (SPF, DKIM, and DMARC) are added to your domain's DNS settings.
Why signing your domain matters:
Proves domain ownership - Inbox providers verify that the email is legitimately sent from your domain, preventing impersonation.
Improves inbox placement - Authenticated emails are more likely to reach the inbox instead of the spam folder.
Removes "via" warnings - Without authentication, providers like Gmail may display messages such as "via omnisend.com" or "via omnisendemail.com," which can reduce recipient trust.
Required by major inbox providers - Gmail and Yahoo require authentication (SPF, DKIM, and DMARC) for bulk email senders.
Note: After signing your domain, a warm-up period is required. Inbox providers treat newly authenticated domains as new senders with no reputation.
💬 Learn how to Sign Your Email Sender Domain in Omnisend.
Warmup: Your First Sends in Omnisend
When you switch ESPs or newly add your sender domain in Omnisend, inbox providers treat you as a new sender. To build trust, you need to gradually increase your sending volume over 2–4 weeks.
How warmup works:
Start with your most engaged Contacts (opened emails in the last 30–90 days).
Increase daily volume by 25–35%.
Monitor open rates, bounces, and spam complaints.
Avoid sudden volume spikes.
If your list is small (<500 subscribers), warm-up may not be necessary.
💬 Learn how to Warm-up Your Domain Manually in Omnisend.
Dedicated IP
Most email service providers (ESPs) use shared IP addresses for multiple customers. One sender's behavior can affect the reputation of others on the same IP.
Dedicated IPs are recommended for high-volume senders only, typically sending 300,000+ emails per week.
💡 Why high sending volume is required for dedicated IP:
A dedicated IP needs a consistent sending volume to maintain a healthy reputation with inbox providers. If you send sporadically or in low volumes, inbox providers treat your IP as inactive or suspicious, which harms deliverability instead of improving it.
💬 Learn What Is a Dedicated IP?
Best Practices for Email Deliverability
Send to Engaged Contacts
Inbox providers (Gmail, Yahoo, Outlook) evaluate subscriber engagement, such as opens, clicks, and replies, to determine whether emails are placed in the inbox or the spam folder.
Contacts who do not engage with your campaigns are more likely to generate spam complaints, bounces, and other deliverability issues.
Best practice: Send campaigns only to contacts who have opened or clicked an email within the last 6–12 months.
💬 Learn how to Improve Deliverability with Engaged Contacts.
Use Segmentation
Sending the same email to your entire contact list may work occasionally. However, personalized content for specific segments typically generates higher engagement and more sales.
The easiest way to personalize your emails is through segmentation, for example, by:
Demographics;
Location;
Past purchases; or,
Position in the sales funnel.
Optimize Email Content
When designing your emails, several best practices can help improve engagement and protect your deliverability.
Clear unsubscribe option: Provide visible opt-out links to reduce spam complaints.
Consistent sender name: Maintain a consistent sender name to build brand recognition.
Healthy image-to-text ratio: Too many images and little text can trigger spam filters.
Avoid spam triggers: Do not use ALL CAPS, excessive exclamation marks, or overly sales-focused language.
No URL shorteners: Avoid URL shorteners, as they are commonly used by spammers to hide their identity.
Important Practice: Always collect consent and only send emails to contacts who voluntarily subscribed.
💬 Learn how to Optimize Email Content for Improved Deliverability.
Understand & Monitor Your Email Delivery Rates
To evaluate your deliverability and identify potential issues, regularly monitor key email performance metrics:
Open rate: Average: ~20%. Higher rates indicate strong inbox placement. If your open rate is below this benchmark, review your sending strategy.
Unsubscribe rate: Average: ~0.2%. Lower rates indicate that your content is relevant to your audience.
Bounce rate: Average: ~0.3%. High bounce rates may indicate poor list quality or outdated contacts.
Spam complaint rate: Average: ~0.03%. This should remain as low as possible to protect your sender reputation.
When testing deliverability improvements, review results across multiple providers. Gmail, Yahoo, and Outlook may handle your emails differently, so performance can vary between inboxes.
💬 Learn more about Omnisend Deliverability Reports.
FAQ
Why are my emails going to spam when my domain is authenticated?
Authentication (SPF, DKIM, DMARC) proves you own the domain, but it doesn't guarantee inbox placement. Email providers also evaluate engagement metrics: open rates, click rates, spam complaints, and bounce rates. Low engagement signals that recipients don't value your emails, triggering spam filters even with perfect authentication. Focus on sending relevant content to engaged contacts.
What spam complaint rate is considered safe?
Keep spam complaint rate below 0.1% (1 complaint per 1,000 emails).To reduce complaints, use Double Opt-In, make unsubscribe links visible, and send only to engaged contacts who expect your emails.
Should my sender email address use a subdomain or root domain?
Your sender email domain must exactly match the domain you authenticated in Omnisend. If you authenticated news.yourdomain.com (subdomain), use [email protected]. If you authenticated yourdomain.com (root), use [email protected]. Subdomains and root domains are not interchangeable; mismatches cause "on behalf of" warnings and harm deliverability.
If you experience any problems with the delivery of your emails or need any recommendations, feel free to reach out to our Support Team via in-app chat or email us at [email protected].