Why are Klaviyo test emails not delivering to Outlook after changing the sending domain?
Michael Ko
Co-founder & CEO, Suped
Published 6 Aug 2025
Updated 18 Aug 2025
8 min read
Switching sending domains in Klaviyo can sometimes lead to unexpected deliverability issues, especially when sending test emails to Outlook. You might find yourself in a frustrating situation where messages simply vanish, not even appearing in spam folders or quarantine. This common problem often points to underlying DNS configuration or sender reputation challenges that arise with a new domain.
When your Klaviyo test emails suddenly stop delivering to Outlook after a domain change, it’s a strong indicator that Microsoft's email systems are blocking your messages before they even reach the inbox or junk folder. This could be due to a variety of reasons, from improperly configured DNS records for your new sending domain to reputation issues that signal a red flag to email providers.
Immediate troubleshooting steps
The first step in troubleshooting these deliverability failures is to perform immediate diagnostic checks on your new sending domain. This includes verifying all crucial DNS records that impact email deliverability. Incorrect or missing records are a frequent cause of emails not being delivered, especially to stricter inboxes like those managed by Microsoft Outlook.
Begin by checking your SPF, DKIM, and DMARC records for the newly configured subdomain. Even if the primary domain has these records set up correctly, a subdomain used for sending emails via Klaviyo will require its own, properly configured DNS entries. I have often seen scenarios where the main domain's records are fine, but the specific subdomain used for marketing emails lacks the necessary authentication.
It's also highly recommended to use Microsoft's Message Trace in Defender. This tool provides detailed logs on what happened to your emails after they left Klaviyo and before they reached the recipient's inbox, including whether they were rejected, quarantined, or delivered. This can often provide the exact reason for non-delivery.
Key initial checks
DNS records: Verify that your new sending subdomain has correct SPF, DKIM, and DMARC records set up in your DNS provider. Klaviyo provides specific records that must be added.
Klaviyo setup: Ensure the sending domain is properly configured and verified within your Klaviyo account settings.
Microsoft Message Trace: Check the logs in Microsoft Defender to see if the emails were received and, if so, why they were not delivered.
Bounce messages: Look for any bounce messages, as these often contain specific error codes or reasons for non-delivery. If you cannot find them, try sending a test to a test email address outside your work domain.
DNS configuration for new sending domains
Understanding DNS and "From" address impact
A crucial, yet often overlooked, detail is the configuration of the From: header domain and its associated DNS records. Even if your emails technically authenticate (pass SPF and DKIM), if the domain specified in your From: header (the address visible to recipients) does not exist or lacks proper MX records, it can trigger spam filters, especially with strict receivers like Outlook. Mail servers often check if the From: header domain has a mail exchange (MX) record, indicating it can receive replies. If it doesn't, the email might be perceived as originating from an unreplyable address, which is a common spam indicator.
When you switch from one subdomain, for example, email.company.com, to another, like e.company.com, it's critical to ensure that Klaviyo is not only delegating the new subdomain correctly but also that its nameservers are returning the necessary MX records for it. Without these, even test emails can be heavily scrutinized or outright blocked by recipient servers.
It's also important to differentiate between the Return-Path (or Mail From) address and the From: header address. The Return-Path is where bounces are sent, and SPF authentication relies on it. This will typically be a Klaviyo-specific subdomain. The From: header is what recipients see and where replies go. While you can send from multiple providers using the same From: header, all replies will route to a single provider. If you intend for replies to go to Klaviyo, their support needs to ensure the new domain supports this via MX records.
Below is an example of what your DNS configuration might look like, highlighting common points of failure or necessary configurations.
DNS Record Type
Old Domain (email.example.com)
New Domain (e.example.com)
Status
SPF (TXT)
v=spf1 include:_spf.klaviyo.com ~all
v=spf1 include:_spf.klaviyo.com ~all
Often missing on new subdomains.
DKIM (CNAME)
k1._domainkey.email CNAME dkim.klaviyo.com
k1._domainkey.e CNAME dkim.klaviyo.com
Required for authentication, needs to be updated for new subdomains.
Crucial for From: header domain validity, often overlooked with ESPs.
The importance of sender reputation
Sender reputation and warming
Even with perfect DNS configurations, changing a sending domain effectively means you're starting with a fresh slate concerning sender reputation. Email Service Providers (ESPs) like Microsoft Outlook are highly sensitive to new domains that suddenly start sending bulk emails. They view this as suspicious behavior that could indicate spamming activity. This is why a domain warm-up process is critical.
When you introduce a new sending domain, it has no prior history. ISPs observe your sending patterns, engagement rates, and how recipients interact with your emails to build a reputation score for that domain. A sudden increase in volume from a new domain can trigger spam filters or even lead to your domain being put on a blocklist (or blacklist). Outlook, in particular, has robust filtering systems designed to protect its users from unwanted mail. For Outlook's new sender requirements, a strong reputation is more vital than ever.
Even for test emails, if the new domain is completely cold, ISPs might be hesitant to accept them. This isn't necessarily a Klaviyo issue but rather how email providers like Outlook assess the trustworthiness of a new sending identity. It's akin to a new person arriving in a community, their actions are initially scrutinized until trust is built. If you want to learn how to improve domain reputation, consider using Google Postmaster Tools.
To mitigate this, a gradual warm-up of the new domain is essential. Start by sending small volumes of emails to highly engaged contacts, slowly increasing the volume over time. This helps build a positive sending history and reputation with ISPs, making them more likely to trust your emails.
Old domain considerations
Established reputation: Likely has a positive sending history with ISPs.
Known configurations: DNS records were already correctly set up and propagated.
Consistent deliverability: Emails were reaching inboxes, including Outlook, without issue.
New domain considerations
Zero reputation: No prior sending history, requiring a warm-up period.
DNS propagation: New DNS changes need time to update globally, potentially causing temporary delivery issues.
ISP scrutiny: ISPs like Outlook may view initial high volume sending from a new domain as suspicious.
Content and email best practices
Content and email best practices
While technical configuration and sender reputation are primary culprits, it's also worth briefly considering the content of your test emails themselves. Although less common for test emails from platforms like Klaviyo, certain content elements can trigger spam filters.
Overly promotional language, excessive use of all caps, too many images without sufficient text, or even specific trigger words can contribute to emails landing in spam or being blocked. Even if these are test emails, the filtering systems are still active. Ensure your test email content is as close to your actual campaign content as possible and adheres to general email marketing best practices.
Also, sending to an unengaged or inactive list, even for tests, can negatively impact your reputation. Maintaining a clean and healthy email list is crucial for long-term deliverability, even with test sends.
Views from the trenches
Best practices
Ensure SPF, DKIM, and DMARC are correctly set for all sending subdomains.
Always include MX records for your 'From:' header domain, even if handled by an ESP.
Implement a gradual warm-up strategy for new sending domains to build trust with ISPs.
Regularly monitor your domain's reputation and deliverability metrics.
Maintain a clean email list to minimize bounces and spam complaints.
Common pitfalls
Forgetting to update all DNS records for new sending subdomains.
Not having MX records for the 'From:' header domain, making it appear unreplyable.
Sending high volumes from a new domain without proper warm-up, triggering spam filters.
Failing to check Microsoft Message Trace for detailed delivery issues.
Assuming authentication is the only factor influencing deliverability.
Expert tips
Use third-party email testing tools to diagnose email header issues and authentication status.
Consult directly with Klaviyo support to verify the subdomain setup and DNS configuration on their end.
Understand the difference between Return-Path (Mail From) and From: header and their respective DNS requirements.
Be patient with DNS propagation; it can take time for changes to reflect globally.
Consider segmenting your test sends to different inbox providers for more granular troubleshooting.
Marketer view
Marketer from Email Geeks says they had a similar issue and checking their Klaviyo setup for logs was the most useful first step.
July 24, 2024 - Email Geeks
Expert view
Expert from Email Geeks says that a common cause is missing SPF records on the new subdomain, even if the apex domain has one.
July 25, 2024 - Email Geeks
Resolving your deliverability issues
Experiencing deliverability issues with Klaviyo test emails to Outlook after changing your sending domain is a common challenge, but one that is usually resolvable with careful attention to detail. The core of the problem often lies in the proper configuration of DNS records, particularly SPF, DKIM, DMARC, and critically, the MX records for your new From: header domain. Additionally, always factor in the need to warm up a new sending domain, even for test sends, to build a positive reputation with ISPs.
By systematically checking your DNS setup, utilizing diagnostic tools like Microsoft's Message Trace, and engaging with Klaviyo support, you can pinpoint and rectify the issues preventing your test emails from reaching Outlook inboxes. Patience and thoroughness in these steps will ensure your email campaigns maintain strong deliverability.
