Why are my low-volume emails going to spam despite having SPF and DKIM set up?
Matthew Whittaker
Co-founder & CTO, Suped
Published 30 Apr 2025
Updated 15 Aug 2025
6 min read
It can be frustrating when your low-volume emails consistently land in the spam folder, even after you've diligently set up SPF (Sender Policy Framework) and DKIM (DomainKeys Identified Mail). While these authentication protocols are fundamental, they are not the only factors email providers consider when determining inbox placement. Even for a small number of emails, providers like Gmail and Outlook look at a broader set of signals.
I've seen this happen frequently, particularly with new or rarely used domains. Authentication is just the first step. To ensure your messages reach the inbox, you need to consider your overall sender reputation, content quality, and recipient engagement. Understanding these elements can significantly improve your deliverability, regardless of your sending volume.
Even with SPF and DKIM correctly configured, DMARC (Domain-based Message Authentication, Reporting, and Conformance) is critical for signaling to receiving mail servers how to handle emails that fail authentication. If DMARC is not set up or is configured with a p=none policy, your emails might still be treated with suspicion, especially for low-volume sends where there isn't a strong historical reputation to lean on. The absence of a robust DMARC policy makes it harder for recipients to trust your domain.
Another crucial factor is your sender reputation (or lack thereof, for low-volume senders). Email providers track your domain's and IP's sending history, complaint rates, bounce rates, and engagement metrics. If your domain is new or you send emails infrequently, you might not have built enough positive reputation. This means mailbox providers are more likely to filter your emails to spam as a precautionary measure. Building domain reputation takes time and consistent positive sending behavior.
For low-volume senders, the challenge is that there aren't enough data points for ISPs to establish trust quickly. They might default to a stricter filtering policy. This is why some emails from new domains go to spam even with correct authentication. It's a chicken-and-egg problem where you need to send emails to build reputation, but those emails might not get delivered initially.
Authentication protocols
SPF and DKIM are foundational. They verify that your emails are legitimately sent from your domain and haven't been tampered with. They are necessary but not sufficient for guaranteeing inbox placement.
SPF: Specifies which mail servers are authorized to send email on behalf of your domain.
DKIM: Adds a digital signature to your emails, allowing recipients to verify that the message hasn't been altered in transit.
Content and recipient engagement
Even if your emails pass authentication, their content can trigger spam filters. Factors like:
Spammy keywords: Words commonly associated with unsolicited email, such as "free," "guarantee," or excessive punctuation.
Poor formatting: Emails with broken HTML, excessively large images, or too many links can appear suspicious.
Missing unsubscribe option: Even for internal communications, omitting a clear unsubscribe link can signal non-compliance with email regulations.
can lead to your emails being flagged. It's not just about what you say, but how you say it and how it's presented. Even with low volume, content quality plays a significant role in avoiding spam folders.
Recipient engagement is arguably one of the most powerful signals to email providers. If recipients open, click, reply to, or move your emails from spam to their inbox, it sends a strong positive signal. Conversely, if emails are consistently ignored, deleted without opening, or marked as spam, your sender reputation will suffer, regardless of your volume.
For low-volume sends, especially to an internal list, actively encouraging recipients to engage with your emails and mark them as not spam is one of the most effective ways to improve deliverability. This positive interaction directly tells the mailbox provider that your emails are desired.
Content pitfalls
Excessive exclamation points: Overuse can trigger filters.
All caps: Commonly used in spam messages.
Over-reliance on images: Too many images with little text can look suspicious.
Bad links: Broken links or suspicious-looking URLs.
Sender IP reputation and infrastructure
The infrastructure you use to send emails plays a major role. If you are sending emails through an in-house system or a lesser-known ESP (Email Service Provider), the IP address reputation might be an issue. Unlike large ESPs that manage millions of sends and have well-established IP reputations, a small or new IP might lack the necessary trust, leading to emails being flagged as spam.
Mailbox providers often consult email blocklists (or blacklists) to determine if an IP address or domain has been associated with sending spam. Even if your domain's authentication is perfect, if the IP address you're sending from is on a blocklist, your emails are likely to go to spam. This is especially true for shared IP addresses, where the actions of other senders can impact your deliverability.
Low-volume senders often face a dilemma when it comes to IP addresses. A dedicated IP needs consistent volume to build reputation, which you might not have. Shared IPs are cheaper and more suitable for low volume, but you inherit the reputation of other senders on that IP. It's a balance that needs careful consideration.
Shared IP addresses
Cost-effective for low volume, as you share the expense and management with others.
Pros: Reputation is built collectively by all senders on the IP, so low individual volume isn't an issue.
Cons: Your deliverability can be negatively impacted by other senders' bad practices on the same IP.
Dedicated IP addresses
Provides exclusive control over your IP's reputation, ideal for high-volume senders.
Pros: You are solely responsible for your reputation, offering more control.
Cons: Requires a substantial and consistent sending volume to warm up and maintain a good reputation. Not suitable for low volume.
Views from the trenches
Even with SPF and DKIM correctly configured, your emails might still land in spam due to other factors. Here's what I've gathered from various discussions.
Best practices
Actively encourage recipients to move emails from spam to the inbox and mark them as 'not spam'.
Maintain consistent sending practices, even for low volumes, to build sender reputation.
Use clear, concise email content and avoid common spam triggers like excessive punctuation or all caps.
Common pitfalls
Relying solely on SPF/DKIM for deliverability, overlooking DMARC and sender reputation.
Sending very low volumes inconsistently, which makes it difficult to establish trust with mailbox providers.
Using a private IP for low-volume sends, which can lead to poor reputation due to insufficient traffic.
Expert tips
Consider that your engagement metrics (like open rates) might differ from what major providers like Gmail track.
Understand that some mailbox providers might whitelist your internal mail, but external providers won't.
Remember that it takes time for a new sending setup (especially with subdomains) to gain trust.
Marketer view
Marketer from Email Geeks says they were likely whitelisting their own mail, which explains why it landed in their organization's inbox but went to spam for external recipients.
2020-04-06 - Email Geeks
Marketer view
Marketer from Email Geeks says the root cause is probably very low volume sent very infrequently to a limited set of inboxes.
2020-04-06 - Email Geeks
The path to inbox success
Getting your low-volume emails into the inbox requires more than just SPF and DKIM. It's about building and maintaining a positive sender reputation over time. This involves having a robust DMARC policy, crafting engaging content, and actively encouraging recipient interaction.
Even with small send volumes, consistency is key. By addressing these factors holistically, you can significantly improve your email deliverability and ensure your important messages reach their intended recipients, not the spam folder.
Gmail and 
Outlook look at a broader set of signals. 
