Why are emails from one account going to spam while emails from another account are not, despite having similar configurations?
Matthew Whittaker
Co-founder & CTO, Suped
Published 11 Jun 2025
Updated 16 Aug 2025
7 min read
It is a head-scratcher when emails from one account consistently land in the spam folder, while messages from another account, seemingly with identical configurations, sail directly into the inbox. This scenario is more common than one might think and highlights the intricate nature of email deliverability. On the surface, you might have the same sender domain, the same content, the same recipient list, and even the same authentication protocols like SPF and DKIM. Yet, one account performs perfectly, and the other struggles.
The key to understanding this discrepancy often lies beyond the basic technical setup. Deliverability isn't just about passing SPF and DKIM. It delves into the nuances of sender reputation, the hidden elements within your email, and how recipients interact with your mail, even across seemingly identical sending streams. We need to look at factors that differentiate email streams at a granular level, which can include subtle variations in tracking domains, IP usage, and historical performance metrics.
Sender reputation nuances
Even with identical SPF and DKIM records, the underlying sender reputation for each account can diverge significantly. Reputation is built over time based on numerous factors, including bounce rates, spam complaint rates, and engagement metrics such as opens and clicks. While your primary domain's reputation might be stable, individual sending streams or subdomains can accumulate their own distinct reputations.
For instance, if one account (Account-1) has historically experienced higher complaint rates or a lower engagement rate compared to Account-2, email service providers (ESPs) like Google or Outlook will assign a lower reputation score to Account-1. This lower score can persist even if you attempt to change tracking links or make minor content adjustments.
It is crucial to monitor your domain and IP reputation using tools like Google Postmaster Tools. These tools provide invaluable insights into your sender reputation, spam rates, and other metrics that influence inbox placement. A consistent negative trend for Account-1, even if minor, can lead to persistent spam filtering.
Account-1 (Spam folder)
Reputation: Lower historical engagement or higher complaint rates associated with this sending identity (even if sharing a main domain).
Tracking domain: The specific tracking domain account1.tool might have a poor individual reputation or have been used for problematic sending in the past.
IP usage: While sharing IPs, Account-1 might be disproportionately routed through (or associated with) an IP with a slightly degraded reputation within the shared pool.
Account-2 (Inbox)
Reputation: Stronger historical performance, lower complaints, and higher engagement contribute to a positive sending identity.
Tracking domain: The tracking domain account2.tool has a clean history and is not associated with problematic sending patterns.
IP usage: This account's traffic tends to be routed through the more performant IPs within the shared pool, or its specific volume doesn't trigger negative thresholds.
Hidden factors and tracking domains
One of the most elusive factors is the reputation of tracking domains. Even if your primary sending domain (e.g., yourcompany.com) is the same across both accounts and has a stellar reputation, the tracking links often use subdomains provided by your email service provider (ESP). For example, account1.your-esp-tracking.com versus account2.your-esp-tracking.com. Each of these subdomains builds its own independent reputation.
If account1.your-esp-tracking.com has a history of being used for problematic email campaigns by other ESP clients, or if it was recently provisioned and inherited a poor reputation, it could be the sole reason for your emails landing in the spam folder. Even if you change it to newaccount1.your-esp-tracking.com, if the new subdomain is too similar or comes from the same problematic pool, it might suffer the same fate. This is especially true if Gmail's filters (or other ISPs) recognize a pattern of similarity to previously identified spam.
Another subtle but impactful factor is the engagement history tied to each account. Even if you send to the same list, how recipients interact with emails sent from Account-1 vs. Account-2 can differ. If recipients are less engaged with Account-1's emails (fewer opens, fewer clicks, more deletes without opening), this negative signal can accumulate and harm its sender reputation, leading to more aggressive spam filtering.
Checking tracking domain reputation
If you suspect your tracking domain, or a subdomain of your ESP's primary domain, might be the culprit, you should check its reputation independently. Many blocklist (or blacklist) checking tools allow you to check domain reputation, not just IPs. Look for any blocklist appearances for the specific tracking subdomains used by Account-1.
New subdomains: If your ESP provisions new tracking subdomains, there's a chance they might have inherited a poor reputation or simply haven't built enough positive history yet. This can be similar to warming up a new IP or domain.
ISP warnings: Many ISPs, including Google, often provide a reason in the email header or a banner in Gmail indicating why a message was marked as spam. Look for phrases like "It is similar to messages that were identified as spam in the past." This often points to content or sending patterns that resemble previous problematic mail.
Content and audience engagement
Even with identical content and list, subtle differences can impact deliverability. Spam filters analyze various aspects of your email, from HTML structure to the plain text version. Any slight variation, such as hidden characters, image-to-text ratio differences, or even the underlying HTML code variations between how Account-1 and Account-2 render the email content, could trigger a spam flag for one account and not the other.
More importantly, even with the same list, the way that list was acquired or maintained for each account might differ. For example, if Account-1's list includes more inactive subscribers or has encountered spam traps in the past, its engagement signals will be poorer, affecting its overall sender reputation. Account-2, despite using the same list, might benefit from better filtering or a more engaged segment of that list.
Recipient behavior is paramount. If recipients of Account-1's emails frequently mark them as spam, even if they initially opted in, this negative feedback is a strong signal to ISPs. Conversely, if Account-2 consistently receives positive engagement (opens, clicks, replies, moving to primary inbox), its positive reputation will grow, ensuring better deliverability. This behavior-based filtering can override seemingly identical technical setups.
Factor
Account-1 (Spam)
Account-2 (Inbox)
Engagement Signals
Higher perceived complaints, lower open/click rates, or more spam trap hits. Might have an existing damaged reputation with certain ISPs.
Consistent positive engagement, low complaints, and high open/click rates over time, leading to a strong sender reputation.
List Quality
Potentially contains more disengaged or invalid addresses, even if the same list name, leading to higher bounces or complaints over time.
Actively managed, highly engaged subscribers with good opt-in practices that consistently provide positive signals to ISPs.
Content Variation
Minor, almost undetectable, differences in HTML structure, hidden text, image usage, or link formatting that trigger spam filters.
Optimized HTML, balanced text/image ratio, and clean formatting that aligns with anti-spam best practices.
Deeper technical checks
While you mentioned using the same 3 IPs across both accounts, it is worth investigating how your ESP rotates or assigns these IPs. Many ESPs use shared IP pools, where your emails are sent from a rotating set of IPs. It is possible that Account-1 is, at certain times, being routed through an IP within the pool that has a slightly poorer reputation or is on a particular blacklist (or blocklist).
To confirm this, you would need to inspect the email headers of emails sent from both accounts that land in different folders. The header will reveal the exact IP address and domain that sent the email. Compare these headers meticulously to identify any subtle differences that might be missed at first glance. Pay attention to the Received lines and Authentication-Results to see if there are any discrepancies in how the mail is being processed or authenticated.
Even with identical SPF and DKIM, DMARC alignment might behave differently under the hood depending on subtle ESP configurations, especially if DMARC verification is failing for one stream but passing for another. These hidden technicalities can be difficult to uncover without direct insight from the ESP or advanced email analysis tools.
Example of email headers to inspect for IP, authentication, and origintext
Received: from mail-tester.com (mail-tester.com [192.0.2.1])
by mx.google.com with ESMTPS id abcdef123456789
for <recipient@gmail.com>
(version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128);
Fri, 02 Feb 2024 10:00:00 -0800 (PST)
Authentication-Results: mx.google.com;
dkim=pass header.i=@yourdomain.com header.s=s1 header.b=abc;
spf=pass (google.com: domain of your@yourdomain.com designates 192.0.2.1 as permitted sender) smtp.mailfrom=your@yourdomain.com;
dmarc=pass (p=none sp=none dis=none) header.from=yourdomain.com
Unraveling the mystery
Unraveling why emails from one account go to spam while another does not, despite similar configurations, often requires a deep dive into factors beyond the obvious. It involves scrutinizing the distinct reputation of tracking domains, analyzing subtle content variations, understanding the nuances of IP rotation within your ESP, and, most critically, examining historical engagement data for each specific sending identity. ISPs are sophisticated in their filtering, looking beyond basic authentication to behavioral patterns and the overall perceived trustworthiness of the sender at every level.
The solution lies in meticulous investigation and potentially segmenting your sending efforts even further, focusing on rebuilding reputation for the problematic account by sending to highly engaged subscribers initially and gradually expanding volume, while continuously monitoring performance metrics. This ensures that each sending stream builds and maintains its own robust reputation, leading to better inbox placement for all your email campaigns.
Views from the trenches
Best practices
Always inspect full email headers for messages landing in spam vs. inbox to identify originating IPs and any authentication failures that might be present.
Segment your recipient lists and send to your most engaged subscribers first from a new or struggling account to build positive reputation signals.
Actively monitor engagement rates (opens, clicks) and complaint rates for each sending account or subdomain individually. Low engagement can silently damage reputation.
Ensure consistency in email content and structure across all sending accounts, paying attention to hidden characters or HTML differences that might trigger filters.
Common pitfalls
Assuming identical configurations guarantee identical deliverability; hidden factors like tracking domain reputation or IP pool variations can cause discrepancies.
Ignoring subtle negative engagement signals for one account (e.g., lower open rates), which accumulate over time and lead to spam folder placement.
Failing to check if a tracking domain or its subdomains are on any domain blocklists (blacklists), which can override otherwise good IP reputation.
Not understanding that even if using the 'same list,' recipient behavior and historical engagement with emails from different accounts can vary significantly.
Expert tips
If the problem persists, try sending a very basic plain-text email with no links from the problematic account to a seed list to isolate if it's content, links, or something else causing the issue.
Consider requesting a new dedicated tracking domain from your ESP for the struggling account, ensuring it has a clean, unused history.
Use email deliverability testing tools to analyze spam scores and inbox placement for both accounts across various mailbox providers, which can highlight specific filter triggers.
Implement feedback loops (FBLs) with major ISPs to quickly identify and remove users who mark your emails as spam, protecting your sender reputation.
Marketer view
Marketer from Email Geeks says checking if subscribers actively opted into both lists independently is crucial because different user expectations can lead to varied engagement and spam complaints.
2022-02-04 - Email Geeks
Marketer view
Marketer from Email Geeks says removing all URLs and sending a test email can help determine if the tracking links are indeed the cause of the spam filtering issues.
