How do I troubleshoot low email open rates, check DKIM configuration, and warm up a new subdomain in Salesforce Marketing Cloud?
Michael Ko
Co-founder & CEO, Suped
Published 5 Aug 2025
Updated 17 Aug 2025
7 min read
Dealing with low email open rates in Salesforce Marketing Cloud (SFMC) can be frustrating. It often points to underlying deliverability issues that need careful investigation. Whether you are seeing a sudden drop or are struggling to establish a good sending reputation with a new subdomain, understanding the root causes is crucial. It’s a multi-faceted challenge, often involving technical configurations, sender reputation, and content quality.
One common scenario involves using a new subdomain or having issues with email authentication. I've seen many marketers in the same position, wondering if a low initial open rate means emails are going straight to spam. It is important to diagnose accurately before making changes. This guide outlines how to troubleshoot low open rates, verify your DKIM setup, and effectively warm up a new subdomain within SFMC.
The steps I recommend will help you identify what might be preventing your emails from reaching the inbox and provide actionable solutions.
When open rates plummet, my first thought goes to basic deliverability checks. A sudden drop, especially on a new sending setup or after a significant change, is a strong indicator of emails landing in the spam folder rather than the inbox. Tools that provide a score may offer some technical insight, but they don't always reflect how inbox providers like Gmail and Yahoo will actually filter your mail.
I focus on evaluating several factors. This includes your list health, the engagement levels of your recipients, and whether you are segmenting your lists effectively. Sending to unengaged or old contacts can quickly damage your sender reputation, leading to lower inbox placement and, consequently, lower open rates. You can find more detailed advice on improving your general email deliverability and open rates in our other resources.
Beyond list quality, content is key. Review your email content for any elements that might trigger spam filters, such as excessive use of all caps, suspicious links, or certain spammy words. Also, ensure your sender name and subject line are clear and trustworthy, as these are the first things recipients see.
Key checks for low open rates
Audience Engagement: Prioritize sending to your most engaged segments first.
List Hygiene: Regularly clean your lists to remove inactive or invalid addresses.
Content Quality: Avoid spam trigger words and ensure your content is valuable.
DKIM (DomainKeys Identified Mail) is a critical email authentication method that helps verify the sender of an email and ensures that the email content hasn't been tampered with during transit. If your DKIM is not properly configured, especially for your From domain, mailbox providers are much more likely to flag your emails as suspicious or outright block them. This is particularly true for bulk senders and is now a strict requirement for Google and Yahoo.
In Salesforce Marketing Cloud, DKIM configuration is typically handled through the Sender Authentication Package (SAP) or through individual domain authentication. If you are using different sender profiles, it is critical to ensure that each profile is configured to sign emails with DKIM. I have found that sometimes a secondary sender profile, perhaps one used for no-reply addresses, might not have DKIM enabled, leading to deliverability issues for those specific sends.
To check your DKIM configuration, you can use online tools that analyze your email headers. These tools will show you if your emails are DKIM signed and whether the signature is valid. If a sender profile is not signing with DKIM, you will need to review your SAP settings or work with Salesforce support to ensure proper DNS records are in place. You can learn more about how to configure email authentication through our guides.
Scenario 1: DKIM not configured
I've seen many instances where a sender profile, particularly one using a root domain like yourcompany.com, isn't properly configured for DKIM signing. This often leads to emails going to spam or being blocked outright by major mailbox providers.
Issue: Emails sent from this profile fail DKIM authentication.
Impact: Reduced deliverability, emails flagged as spam.
Action: Configure DKIM for the root domain in SFMC via SAP or custom domain authentication.
Scenario 2: DKIM configured on subdomain
Conversely, a sender profile utilizing a dedicated subdomain (e.g., mail.yourcompany.com) might already have DKIM correctly configured as part of the SAP setup. Switching to this profile could resolve immediate authentication issues.
Observation: Emails from this profile pass DKIM checks.
Implication: This profile is generally more reliable for sending.
Consideration: Ensure the Reply-To address is a real mailbox.
Example DKIM CNAME recordDNS
mail.mycompany.com. 1800 IN CNAME example.s7.exacttarget.com.
Warming up a new subdomain
Warming up a new subdomain is a non-negotiable step for establishing a good sender reputation, especially when you are sending through a platform like Salesforce Marketing Cloud. A new subdomain, even if part of your existing domain, starts with a neutral or unknown reputation. Sending large volumes of emails immediately from it can trigger spam filters and lead to your subdomain or even your IP being added to a blocklist (or blacklist).
The warming process involves gradually increasing your email volume over time, starting with your most engaged subscribers. This allows mailbox providers to recognize your sending patterns as legitimate and build trust in your new sending infrastructure. It is about proving you are a reliable sender. For a comprehensive guide, check our article on how to warm up a new subdomain.
If you are switching from an old sender profile to a new subdomain that is configured with SAP in SFMC, you will almost certainly need to warm it up. While switching an alias on an already warmed domain might not require a full warm-up, changing the underlying domain (even to a subdomain) is treated as a new sending entity by mailbox providers. This applies whether you are using a shared IP or a dedicated IP through Salesforce Marketing Cloud.
Warming Stage
Volume Guidance (Daily)
Audience Focus
Metrics to Monitor
Week 1
500-1,000 emails
Highly engaged subscribers
Open rates, bounce rates, spam complaints
Week 2
2,000-5,000 emails
Recently engaged, moderate activity
Inbox placement, reputation at ISPs
Week 3+
Gradual increase (up to daily volume)
Broader engaged segments
Overall deliverability, open and click rates
Advanced considerations and continuous monitoring
Beyond DKIM and warm-up, several other technical and strategic elements contribute to email deliverability. Implementing SPF (Sender Policy Framework) and DMARC (Domain-based Message Authentication, Reporting, and Conformance) records is essential. These authentication protocols work together with DKIM to prove your legitimacy and protect your domain from spoofing and phishing attacks. You can explore how to troubleshoot and fix these settings.
I also recommend ensuring that your From address is a real, active mailbox capable of receiving replies. Sending from a no-reply address that isn't monitored can negatively impact subscriber trust and engagement. Salesforce Marketing Cloud's Reply Mail Management (RMM) feature can help you manage replies even when using a dedicated sending subdomain, ensuring replies are directed to an appropriate inbox.
Finally, continuous monitoring of your email deliverability metrics, including bounces, spam complaints, and overall open and click-through rates, is vital. Tools like Google Postmaster Tools provide valuable insights into your domain and IP reputation, allowing you to react quickly to any emerging issues. Consistent monitoring helps maintain a healthy sending reputation over time.
Views from the trenches
Best practices
Segment email lists based on engagement levels to send to the most active subscribers first.
Always use a sender profile that is correctly configured with DKIM for all email sends.
Ensure the 'From' email address is a real, monitored inbox that can receive replies.
Implement a gradual warm-up plan when introducing any new sending subdomain or IP address.
Common pitfalls
Relying solely on generic email tester scores without checking actual inbox placement.
Sending high volumes of email from a new, unwarmed subdomain, which damages sender reputation.
Neglecting to configure DKIM for all sender profiles, leading to authentication failures.
Not monitoring email bounce rates and spam complaint rates from major ISPs.
Expert tips
Use Salesforce Marketing Cloud's Reply Mail Management (RMM) to direct replies from sending subdomains.
Regularly review your email content for spam trigger words to improve inbox placement.
If moving to a new subdomain, assume a warm-up is needed, even if the main domain is established.
Leverage DMARC reports to identify authentication failures and gain insights into email delivery.
Marketer view
Marketer from Email Geeks says a sudden drop in open rates after two hours usually indicates emails are going to spam, despite good Mailtester scores.
2024-08-20 - Email Geeks
Expert view
Expert from Email Geeks says generic mail tester platforms do not always reflect real deliverability, and it's better to focus on list health and engagement.
2024-08-20 - Email Geeks
Summary of best practices
Troubleshooting low email open rates in Salesforce Marketing Cloud requires a systematic approach, addressing both technical configurations and content strategy. By ensuring your DKIM is properly configured across all sender profiles and carefully warming up any new subdomains, you lay a strong foundation for consistent email deliverability.
Remember, email deliverability is an ongoing effort, not a one-time fix. Regular monitoring and adherence to best practices will help you maintain a healthy sender reputation and ensure your marketing messages reach your audience's inboxes effectively.
Google and 
Yahoo.
