Key facts
- SPF, DKIM, and DMARC are three separate authentication records added to your domain's DNS settings, and major providers like Gmail and Yahoo require at least SPF and DKIM to be correctly set up for reliable inbox delivery.
- A domain with no sending history, or one that suddenly sends a large volume of email after months of little activity, looks suspicious to spam filters even with correct authentication in place.
- A high bounce rate, sending to email addresses that no longer exist or were never valid, is one of the fastest ways to damage a sending domain's reputation, since it is treated as a strong spam signal.
- Low engagement, recipients who never open or click, and especially recipients who mark a message as spam, both feed directly into how mailbox providers score your future emails from that same domain.
- Free tools like Google Postmaster Tools and Mail Tester check your authentication setup and give a reputation score, making them a faster diagnostic than guessing which specific factor is causing spam placement.
Start With SPF, DKIM, and DMARC
Before looking at anything else, confirm your domain has correctly configured SPF, DKIM, and DMARC records. These are three separate DNS entries that together prove to receiving mail servers that an email claiming to come from your domain was actually authorized to be sent by whatever service sent it, whether that is your website's contact form, a marketing platform, or your regular email provider.
SPF lists which mail servers are allowed to send on behalf of your domain. DKIM adds a digital signature to each message that proves it was not altered in transit and really did originate from an authorized sender. DMARC tells receiving providers what to do with a message that fails either check, and also reports back to you when something claiming to be from your domain fails authentication, which can reveal both a technical misconfiguration and, occasionally, someone impersonating your domain.
A free tool like Mail Tester or Google Postmaster Tools checks all three at once and reports specifically which one is missing or misconfigured, which is far faster than manually inspecting DNS records if you are not familiar with reading them directly.
Your Sending Domain Has a Reputation, and It Can Be Damaged
Even with authentication correctly set up, mailbox providers track a reputation score for your sending domain and, separately, for the specific service or IP address sending on your behalf. A domain with little sending history, or one that suddenly jumps from sending a handful of emails a week to a large batch all at once, looks unusual to spam filters, since that pattern resembles a compromised account or a new spam operation.
Bounce rate is one of the fastest ways to damage this reputation. Sending repeatedly to addresses that no longer exist, that were never valid, or that were collected without genuine opt in, tells mailbox providers your list quality is poor, which lowers trust in everything else you send, including to your genuinely engaged, opted in recipients.
Engagement works the same way in reverse. Recipients who consistently open and click your emails signal to providers that your messages are wanted, while recipients who never open, or worse, actively mark a message as spam, signal the opposite. A domain with a run of low engagement sends can see its deliverability degrade even for a completely legitimate, well written email sent afterward.
Content and Formatting Still Play a Role
Beyond authentication and reputation, the content of the email itself can trigger spam filtering. A subject line or body heavy with promotional language, excessive punctuation, or phrases commonly associated with spam can push a message toward the spam folder even from a well reputed domain, though this factor generally matters less than authentication and reputation issues.
An email with a very high ratio of images to text, or one built almost entirely as a single large image with little actual readable text, can also raise flags, since that pattern is common in spam designed to avoid text based filtering. Keeping a reasonable mix of real text alongside any images reduces this risk.
Too many links, especially links to unfamiliar or newly registered domains, can also count against a message. If your email includes tracking links through a third party service, make sure that service itself maintains a good sending reputation, since a shared link shortening or tracking domain with a poor reputation can drag down deliverability for messages that use it, independent of your own domain's standing.
What To Do Next
Fix authentication first, since it is foundational and a missing or broken SPF, DKIM, or DMARC record can single handedly cause consistent spam placement regardless of everything else being done correctly. Then review your list quality and recent bounce rate, removing invalid addresses before they continue to damage your reputation with every additional send.
If authentication and list quality both check out, look at engagement trends over the last several sends and consider whether your content, subject lines, image ratio, or link patterns resemble common spam characteristics, adjusting gradually rather than overhauling everything at once so you can tell which change actually helped.
SearchPod sets up proper email authentication and monitors deliverability as part of every email marketing engagement, priced according to the scope of automation and the size of the list involved. Reach out at /get-proposal for a free proposal, which is generally ready the next business day.
Related questions
Free tools like Mail Tester and Google Postmaster Tools check all three authentication records at once and report specifically which are missing or misconfigured. Most email marketing platforms also provide their own setup instructions and often a built in verification check for these records once you add them to your domain's DNS settings.
Yes. Sender reputation accumulates over time rather than resetting with each send, so a period of high bounces can continue affecting deliverability for subsequent, unrelated sends until your reputation recovers. Regularly removing invalid addresses from your list before sending is the most effective way to prevent this ongoing damage, and it is worth doing even between planned campaigns.
A new domain does not have an established reputation yet, which makes providers more cautious rather than automatically hostile. Warming up gradually, starting with smaller, highly engaged sends and increasing volume over time, generally builds a healthy reputation faster than sending a large volume immediately from a brand new domain.
Not necessarily by itself, but a very high ratio of image content to actual text, or an email built almost entirely as one large image, can be a contributing factor to spam filtering. A reasonable balance of real text alongside images is generally a safer pattern than an email with little to no readable text content.
Generally yes, after a reasonable number of attempts. Continuing to email consistently unengaged recipients drags down your overall engagement rate, which mailbox providers weigh when deciding where your future emails land, even for recipients who do actively want and open your messages, so trimming an unengaged segment often improves delivery for everyone else on the list.
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