What are best practices for improving email deliverability when using Mautic and SMTP.com?
Matthew Whittaker
Co-founder & CTO, Suped
Published 27 Apr 2025
Updated 17 Aug 2025
7 min read
Navigating email deliverability can be challenging, especially when using a marketing automation platform like Mautic alongside a dedicated SMTP service such as SMTP.com. It's common to encounter situations where emails, despite proper authentication, land in spam folders. This is particularly frustrating when you're diligent with your SPF, DKIM, and DMARC records and see no obvious issues like being on a public blacklist (or blocklist).
The complexity often arises from various factors beyond just authentication, including your sending infrastructure, content, and recipient engagement. When using Mautic, for instance, issues can stem from how your tracking domains are configured or the types of links and images embedded in your emails.
If you're seeing messages like "Why is this message in spam?" but lack spam complaints in Google Postmaster Tools, it signals that the problem might lie in subtleties of your email campaigns. We'll explore actionable strategies to enhance your email deliverability, specifically when Hotmail (Microsoft) and Yahoo inboxes are proving to be challenging.
Optimize your domain alignment and tracking
One of the most critical aspects to address when using Mautic and an external SMTP provider like SMTP.com is ensuring consistent branding and reputation across all sending domains and subdomains. If your emails are sent from one domain (e.g., Earthledger.one) but Mautic's tracking links or embedded images reference a different domain (e.g., outbound.smartmind.one), this can raise red flags with mailbox providers.
Mailbox providers, particularly those like Microsoft and Yahoo, scrutinize every element within an email to determine its legitimacy. A mismatch between the sending domain and the tracking domain can be perceived as an attempt to hide the true origin of the email, leading to filtering into the spam folder. To mitigate this, configure Mautic to use a tracking domain that is a subdomain of your primary sending domain.
This setup, often referred to as a custom tracking domain, ensures that all links and images within your emails appear to originate from the same trusted entity as the email itself, improving your overall domain reputation.
Content quality and recipient engagement
The content of your emails plays a significant role in deliverability. While striking images and rich HTML can be engaging, overly complex or heavily image-based emails can sometimes trigger spam filters. It's worth experimenting with your email content, particularly if you are experiencing issues with specific providers like Hotmail and Yahoo.
Consider sending a portion of your emails as plain text or with a very minimal HTML structure. This helps determine if your current email design, image links, or text-to-image ratio is contributing to your deliverability challenges. Additionally, ensure your email content adheres to general email deliverability best practices, avoiding spammy keywords, excessive exclamation points, and poor formatting.
Recipient engagement is another critical factor. Even if your emails are technically perfect, low engagement (low open rates, low click-through rates) or high negative signals (deletes without opening, moving to junk, manual spam reports) can harm your sender reputation over time. Regularly clean your email list to remove inactive subscribers, and implement a double opt-in process to ensure you're only sending to engaged recipients.
Content evaluation
Review your email content for potential spam triggers, which could include: too many images relative to text, hidden text, excessive use of bolding or capitalization, and suspicious link structures. Test with plain text emails to isolate content issues.
Engagement analysis
Segmentation: Send relevant content to segmented lists to improve engagement.
Frequency: Adjust your sending frequency to avoid overwhelming subscribers.
Feedback loops: Actively monitor and respond to feedback loops if your SMTP provider offers them.
Monitor and troubleshoot with mailbox provider tools
Even with perfect authentication and no apparent blocklist (or blacklist) issues, some mailbox providers, like Microsoft Outlook and Hotmail, or Yahoo Mail, can be more stringent. Each provider has its own proprietary spam filtering algorithms, which weigh various signals, including sender reputation, content, and recipient behavior. While Google Postmaster Tools provides excellent insights for Gmail, you'll need to consult the postmaster pages for Microsoft and Yahoo for specific insights into your deliverability with their services.
These postmaster portals offer dashboards and tools that can help diagnose issues unique to their platforms. For example, Hotmail's SmartScreen filter is highly sensitive to content, sender reputation, and user feedback. Yahoo also heavily relies on user engagement and the overall quality of the sending IP and domain.
If you're using a shared IP address from SMTP.com, your deliverability can be impacted by the sending practices of other users on that same IP. While SMTP.com typically manages its IP reputation rigorously, sustained issues with specific providers might warrant a discussion with their support team about your sending patterns or considering a dedicated IP if your volume justifies it. Remember that improving sender reputation is an ongoing process.
Beyond authentication and public blocklists
While you've confirmed your SPF, DKIM, and DMARC are in order, it's worth a deeper look into the specifics of your DMARC reports. Sometimes, a DMARC pass doesn't tell the whole story, particularly if there are alignment issues or subtle errors that only advanced DMARC analysis can reveal. Ensure your SMTP.com setup correctly handles DMARC alignment for both SPF and DKIM for your sending domain.
It's also crucial to understand that not being on a public blocklist (or blacklist) doesn't mean your emails are entirely safe. Many ISPs maintain their own internal blocklists (or blacklists), which are not publicly accessible. These internal lists are often triggered by consistent negative engagement from recipients, or content that looks suspicious to their filters. This is why a holistic approach to improving email deliverability is essential.
Regularly review your email sending practices against common anti-spam guidelines. This includes avoiding excessive links, cloaking, or anything that could be interpreted as deceptive. Always provide a clear and easy unsubscribe option, and honor unsubscribe requests promptly. These seemingly small details contribute significantly to your long-term sender reputation and help keep your emails out of the spam folder.
Continuous optimization and testing
To truly get ahead, embrace a mindset of continuous optimization and testing. Email deliverability isn't a set-it-and-forget-it task; it requires ongoing vigilance and adaptation.
Use an email deliverability tester to check your emails before sending them out to a large audience. These tools can flag potential issues with content, formatting, and authentication that might trigger spam filters. This proactive approach can save you from widespread deliverability headaches.
Ultimately, landing in the inbox consistently with Mautic and SMTP.com involves a combination of technical configuration, smart content choices, and diligent monitoring. By addressing the nuances of domain alignment, content quality, and specific ISP requirements, you can significantly improve your email deliverability and ensure your messages reach their intended recipients.
Remember, the goal is to build and maintain a strong sender reputation across all mailbox providers. This comes from sending valuable content to an engaged audience, backed by a robust and correctly configured technical infrastructure.
Views from the trenches
Best practices
Always use a custom tracking domain in Mautic that aligns with your sending domain to avoid flags from mailbox providers.
Test emails with no links and no images to a small sample to see if Google delivers them to the inbox or spam.
Regularly monitor your domain reputation in Google Postmaster Tools and specific postmaster sites for Hotmail and Yahoo to identify issues.
Maintain a clean email list and prioritize sending to engaged recipients to improve overall sender reputation.
Consider engaging with SMTP.com support if specific deliverability challenges persist, as they can offer insights into their IP reputation.
Common pitfalls
Using different domains for email sending and tracking, which can lead to emails being marked as suspicious by ISPs.
Overly complex or image-heavy email content, which can trigger spam filters, especially with Hotmail and Yahoo.
Neglecting to monitor domain reputation metrics beyond DMARC compliance, missing subtle signs of filtering.
Ignoring low engagement rates or not removing unengaged subscribers, which negatively impacts sender reputation over time.
Assuming that being off public blocklists guarantees inbox placement, overlooking internal ISP blocklists (or blacklists).
Expert tips
Hotmail (Microsoft) and Yahoo have distinct, often stricter, filtering criteria compared to Gmail.
While Mautic is free, using your own domain for link tracking is essential for brand consistency and deliverability.
Even if DMARC, SPF, and DKIM are compliant, content and sender behavior are crucial for inbox placement.
A "Why is this message in spam?" warning without Google Postmaster complaints indicates content or engagement issues.
Always aim for relevant content for segmented lists and adjust sending frequency to enhance recipient engagement.
Marketer view
Marketer from Email Geeks says to try sending text-based emails to see if that improves deliverability.
2023-09-09 - Email Geeks
Marketer view
Marketer from Email Geeks says to check the domain reputation chart in Google Postmaster Tools, as Google's filters consider many factors like links, content, and audience.
