Why is my customer service email being flagged as spam by Google even with DKIM and SPF?
Matthew Whittaker
Co-founder & CTO, Suped
Published 9 Jul 2025
Updated 19 Aug 2025
8 min read
It's a common frustration to see your customer service emails, essential for business communication, land in the spam folder, especially when you've diligently set up authentication protocols like SPF and DKIM. You'd expect these measures to guarantee inbox delivery, but the reality can be more complex. Google's spam filters are sophisticated, evaluating many signals beyond just basic email authentication.
Even with perfect SPF (Sender Policy Framework) and DKIM (DomainKeys Identified Mail) records, other factors can influence how your emails are perceived. These authentication methods verify that an email is genuinely from your domain and hasn't been tampered with, which is crucial for preventing spoofing and phishing. However, they don't tell the whole story to an inbox provider like Google.
If your customer service emails are consistently flagged as spam, it's time to look beyond authentication. This issue can stem from various sources, ranging from subtle technical misconfigurations to the content of your emails and the behavior of your recipients.
Your sender reputation is arguably the most significant factor determining whether your emails land in the inbox or the spam folder. Authentication, while important, is just one component that contributes to this reputation. Inbox providers assign a score to your sending domain and IP address based on numerous signals.
Factors like how recipients engage with your emails (opens, replies, clicks), how often your emails are marked as spam, and the volume and consistency of your sending all play a role. A sudden spike in volume, a high number of bounces, or frequent spam complaints can quickly degrade your reputation, leading to legitimate emails being blocklisted or sent to spam (or junk). Google's filters are highly sensitive to these behavioral metrics. Even a low volume of spam complaints can significantly impact your deliverability to Gmail.
To gauge your standing, leverage tools like Google Postmaster Tools. This free service provides detailed insights into your domain's reputation, spam rates, IP reputation, and authentication status, helping you pinpoint specific issues affecting your deliverability.
Content, audience, and DMARC alignment
Even with strong authentication, the content of your emails can trigger spam filters. Overly promotional language, excessive use of all caps, suspicious links, or certain attachments can flag your message. Similarly, issues with your email list can lead to problems. Sending to old, unengaged, or invalid email addresses can increase bounce rates and spam complaints, negatively impacting your sender reputation.
For customer service emails, ensure clarity and avoid anything that might be mistaken for marketing. A clean, concise message with a clear call to action (e.g., Reply to this email) is best. Make sure your HTML best practices are followed to avoid any formatting issues that might look suspicious. Always include an easy way for recipients to opt out, even from transactional messages, where appropriate. While not legally required for transactional emails in most regions, providing a clear unsubscribe option can reduce spam complaints.
Consider the sender address itself. While customerservice@yourdomain.com is appropriate for support, ensure it's not confused with a generic or no-reply address typically used for marketing or automated notifications. Using Gmail, Yahoo, or Outlook public domain email addresses as your From address for business communication is also discouraged and can lead to spam flagging.
Even if your SPF and DKIM pass, your DMARC policy (Domain-based Message Authentication, Reporting, and Conformance) could be failing due to alignment issues. DMARC requires that the domain in the From header (the one users see) aligns with the domains used for SPF or DKIM authentication. If you're sending through a third-party service, the authenticating domain might not perfectly match your visible From address, causing DMARC to fail and leading to spam placement or even rejection. This is a common reason emails land in spam.
Domain association and hidden technical factors
Sometimes, the problem isn't your email authentication but rather how Gmail perceives the relationship between your various domains or sending infrastructure. If your customer service emails are sent from customerservice@companyname.com but your marketing campaigns use companynameco.com (or vice versa), Google might associate these domains, especially if they link to the same core website (e.g., companyname.com). This intermingling means that reputation issues on one domain could inadvertently affect the deliverability of emails from the other, even if their authentication is technically distinct.
Another subtle issue can arise if the Reply-To domain in your email headers differs significantly from the From domain. While Gmail typically distinguishes between spam labels and phishing warnings, a mismatch can sometimes trigger a ‘be careful with this message’ warning. This can negatively affect recipient trust and engagement, indirectly influencing spam placement.
It's also worth investigating any potential blacklist (or blocklist) listings for your sending IP or domain. While direct blacklisting is less common for legitimate customer service emails, issues elsewhere in your sending infrastructure or historical sending patterns could lead to a listing. Even if you're not on a major public blacklist, internal reputation systems at Google might still flag your domain or IP.
Finally, ensure that your DNS records are correctly configured beyond just SPF and DKIM. This includes Reverse DNS (PTR) records for your sending IPs, which help receiving mail servers verify that the IP address is authorized to send email for your domain. While less common for third-party sending services, it's a critical component for direct senders.
Proactive monitoring and maintenance
Proactive monitoring and maintenance are crucial to preventing and resolving deliverability issues. Don't wait until complaints surface.
Best practices for deliverability
Monitor: Regularly check Google Postmaster Tools for domain reputation, spam rates, and authentication errors. This provides invaluable insight into how your emails are performing with Google.
Authenticate: Ensure DMARC, DKIM, and SPF records are correctly configured and aligned, especially if using a third-party sender. Verify alignment for the domain in the From header.
Segment: Separate your transactional or customer service emails from marketing campaigns. This helps isolate reputation issues and ensures critical communications are less affected by promotional sending.
Implement continuous DMARC monitoring. This will give you detailed reports on email authentication failures, providing clues to what might be going wrong. These reports show you which emails pass or fail SPF, DKIM, and DMARC checks, and from which IP addresses they are being sent. Analyzing these reports can reveal if a legitimate sending source is not properly configured, or if there's unauthorized use of your domain. Pay close attention to DMARC verification failed errors.
Troubleshooting actions
Analyze headers: Obtain the full email header of a message that landed in spam. Look for Authentication-Results and X-Google-Smtp-Source headers for specific spam filter reasons. This is a common way to diagnose why emails are sent to spam.
Check email content: Review the content for common spam triggers, including suspicious links or attachments. Avoid overly aggressive or sales-oriented language in customer service emails. Ensure all links are valid and not on any blocklists.
Furthermore, regularly clean your email lists to remove inactive or invalid addresses. Sending to engagement traps (old, unused email addresses that become spam traps) can severely damage your reputation. Ensure that any marketing campaigns you run from associated domains (or even entirely separate domains if they link back to your core brand) also adhere to best practices to avoid negatively impacting your primary customer service domain. This includes providing clear unsubscribe options, as mandated by Google and Microsoft's new sender requirements.
Summary
It's understandable to be perplexed when your customer service emails are flagged as spam, even with SPF and DKIM correctly configured. However, email deliverability is a complex ecosystem where authentication is just the foundation.
The key lies in understanding that inbox providers, especially Google, use a holistic approach to determine inbox placement. This includes scrutinizing your sender reputation, the quality and content of your emails, recipient engagement, list hygiene, and potential issues arising from intermingled domain use or DMARC alignment failures. These factors can collectively outweigh the positive signal from SPF and DKIM if not managed properly.
By proactively monitoring your sender reputation, ensuring DMARC alignment, maintaining clean email lists, crafting clear and non-promotional content for customer service, and segmenting your email sending, you can significantly improve your chances of reaching the inbox. A comprehensive approach to email deliverability ensures that your vital customer communications aren't lost in the spam folder.
Views from the trenches
Best practices
Maintain an excellent sender reputation by keeping spam complaints low and engagement high.
Regularly monitor your domain and IP reputation using tools like Google Postmaster Tools.
Ensure DMARC is properly configured with a strong policy (quarantine or reject) and that SPF and DKIM domains align with your "From" header domain.
Segment your email sending infrastructure to separate transactional/customer service emails from marketing campaigns.
Clean your email lists frequently, removing inactive or invalid addresses to reduce bounces and spam trap hits.
Ensure all outgoing emails, especially marketing ones, include clear and easy-to-find unsubscribe options.
Audit your email content to remove spam trigger words, suspicious links, or overly promotional phrasing in customer service messages.
Common pitfalls
Assuming SPF and DKIM alone guarantee inbox delivery, neglecting sender reputation and content quality.
Sending emails with inconsistent "From" and "Reply-To" domains, which can trigger phishing warnings.
Using generic public domain email addresses (e.g., @gmail.com) for business customer service.
Not monitoring DMARC reports, missing critical insights into authentication failures or domain misuse.
Sending to outdated or unengaged email lists, leading to high bounce rates and spam complaints.
Failing to provide visible and functional unsubscribe links in marketing emails, increasing spam reports.
Allowing marketing activities on one domain to negatively impact the reputation of a related customer service domain.
Expert tips
Always retrieve and analyze the full email headers of messages that land in spam; they often contain specific reasons for filtering.
If using a third-party sender, ensure their authentication settings (SPF, DKIM) align directly with your "From" domain, not just their own.
Consider setting up a dedicated IP address for your customer service emails if volume is high, to isolate its reputation from other sending activities.
Regularly test your email deliverability to major inbox providers using a robust email testing tool.
Educate your customer service team on proper email etiquette and content guidelines to avoid triggering spam filters inadvertently.
For shared sending IPs, investigate if other users on that IP are causing reputation issues.
Actively encourage recipients to whitelist your customer service email address and move emails from spam to inbox.
Expert view
Expert from Email Geeks says that knowing the exact domains used for SPF and DKIM authentication is critical, as they don't necessarily have to be the same as the visible From address.
2020-12-02 - Email Geeks
Expert view
Expert from Email Geeks says that Google can recognize when different domains, like COMPANYNAME.com and COMPANYNAMECO.com, belong to the same entity, especially if they are linked through the same Gsuite account or shared URLs.
Google.
Gmail, 
Yahoo, or 
Outlook public domain email addresses as your From address for business communication is also discouraged and can lead to spam flagging.
Microsoft's new sender requirements.
