Why are my low-volume emails going to spam despite having SPF and DKIM set up?

Key findings

• Authentication not enough: Passing SPF and DKIM is necessary, but not sufficient to guarantee inbox placement, particularly for low-volume sending.
• Low volume impact: Infrequent, low-volume sending can make it harder for ISPs to establish a positive sender reputation for your domain, leading to emails being flagged as suspicious, even with proper authentication. This is especially true for new domains or subdomains.
• Engagement signals: Recipient engagement (opens, clicks, replies, moving from spam to inbox) is a strong signal to ISPs about the legitimacy of your emails. Lack of these signals, or negative signals (spam complaints), can lead to spam folder placement.
• Internal vs. external filters: Internal organizational inboxes might whitelist your domain, causing emails to land in the inbox, while external providers like Gmail or Outlook apply stricter filtering based on broader reputation metrics.
• Content quality: Even authenticated emails can be filtered if the content triggers spam filters (e.g., suspicious links, excessive images, spammy keywords).

Key considerations

• Domain reputation building: For low volumes, consistently sending engaging content can gradually build a positive domain reputation. This is a long-term strategy.
• Encourage positive engagement: For internal emails, actively ask recipients to move emails from spam to inbox or add your address to their contacts. This direct engagement helps train filters. Consider how engagement impacts email deliverability.
• Sending infrastructure: Ensure your sending system, even if in-house, is configured to best practices and avoids behaviors that mimic spam. Using a shared IP from a reputable provider is generally better for low volumes than a dedicated IP, which requires consistent high volume to maintain its reputation.
• Monitor deliverability: Regularly check inbox placement across various email providers. Tools like Google Postmaster Tools can offer insights into your domain's reputation with Google.

Key opinions

• Subdomain challenges: Marketers moving to new subdomains often report initial deliverability issues, even if their main domain performs well.
• Whitelisting effect: Internal whitelisting within an organization can create a false sense of security, as external providers like Gmail apply different, often stricter, filtering rules.
• Sender reputation takes time: Building trust with ISPs for new or low-volume sending profiles requires time and consistent positive engagement, regardless of authentication. For more insights, refer to common reasons emails go to spam.
• Low volume sensitivity: Very low and infrequent sending can be a deliverability hurdle because it doesn't provide enough consistent data for ISPs to build a reliable reputation.
• Engagement as a fix: Actively encouraging recipients to move emails from spam or engage with content is often cited as a direct way to improve deliverability for small lists.

Key considerations

• Sending system audit: Review your sending system (especially if in-house) to ensure it's not inadvertently mimicking spam characteristics. If using a custom system, make sure its mail looks like legitimate ESP mail.
• Recipient outreach: For small, known lists, a direct request to whitelist or move emails from spam can significantly impact deliverability.
• Consistent engagement: Even with low volume, try to ensure recipients open and click. This positive interaction helps train ISP filters over time. Consistent monitoring of marketing email deliverability is key.
• Patience is key: Deliverability can improve over time as ISPs learn to trust your sending patterns and recipient engagement, especially with positive signals.

Key opinions

• Engagement measurement: Your internal engagement metrics (opens, clicks) may differ from how ISPs, especially large ones like Gmail, measure engagement. ISP-specific engagement signals are paramount.
• Low volume reputation: Very low volume and infrequent sending to a limited set of inboxes makes it challenging to establish a consistent, positive sender reputation with ISPs.
• No private IP for low volume: Using a dedicated (private) IP address for very low sending volumes is generally a bad idea, as it can struggle to build the necessary reputation without sufficient volume.
• Proactive recipient action: The most effective fix for low-volume issues is often a few rounds of recipients actively pulling emails out of spam folders and marking them as "not spam".
• Content and opt-in: Assess if your sending system looks like legitimate ESP mail or closer to spam, and review your address collection processes and opt-in status, even for internal lists. These are critical expert tips to improve deliverability.

Key considerations

• Understand ISP algorithms: Recognize that different mailbox providers have their own unique algorithms for spam filtering, and internal engagement metrics may not translate directly to external inbox placement.
• Sender reputation nuances: For low volumes, the initial reputation of a new subdomain can be particularly fragile. It requires consistent positive signals to overcome this. This applies even if your DMARC, SPF, and DKIM pass authentication.
• Focus on engagement campaigns: Design emails specifically to encourage opens, clicks, and positive interactions from recipients, especially during the initial phases of sending from a new or low-volume domain.
• Content relevance: Ensure the email content is highly relevant and anticipated by the recipients to maximize engagement and minimize spam complaints.

Key findings

• Beyond authentication: Authentication standards like SPF and DKIM verify sender identity but do not guarantee inbox delivery. ISPs evaluate sender reputation as a primary factor.
• Sender reputation complexity: Reputation is built over time based on various factors, including IP reputation, domain reputation, spam complaint rates, bounce rates, and user engagement (opens, clicks, replies, FBLs).
• Volume and consistency: New senders or those with inconsistent, low volumes often face greater scrutiny from filters due to a lack of established positive sending patterns. This is highlighted in guidelines for Outlook's new sender requirements.
• Engagement as a trust signal: Positive engagement from recipients acts as a strong signal to ISPs that your emails are valued and not spam.
• Content guidelines: Adhering to content best practices (e.g., clear subject lines, relevant body content, working links, unsubscribe options) is crucial for avoiding spam filters.

Key considerations

• DMARC implementation: While SPF and DKIM are set up, ensure DMARC is also correctly implemented and aligned. DMARC provides instructions to ISPs on how to handle emails that fail SPF or DKIM validation. A DMARC fail error can be a significant issue.
• Sender warm-up: For new domains or subdomains, gradually increasing sending volume (warming up) helps build reputation before sending to full lists. Even for low volume, this phased approach can be beneficial.
• Monitor feedback loops: Register for ISP feedback loops (FBLs) to receive reports on spam complaints, enabling you to identify and remove problematic recipients from your list. This helps maintain a good Google Postmaster Tools domain reputation.
• Compliance with guidelines: Stay updated with and comply with sender guidelines published by major ISPs like Gmail and Outlook, which often include requirements beyond basic authentication.