Why do SendGrid transactional emails go to spam but campaign emails go to inbox?
Matthew Whittaker
Co-founder & CTO, Suped
Published 21 May 2025
Updated 17 Aug 2025
8 min read
It can be perplexing when your transactional emails sent via SendGrid consistently land in the spam folder, yet your campaign emails, seemingly from the same sender and IP, arrive in the inbox. This scenario often suggests a deeper nuance in how mailbox providers assess different email types and how your email service provider (ESP) handles them. It is not always as straightforward as checking the IP or domain name alone.
The distinction between how transactional and campaign emails are treated, even when originating from the same platform, hinges on several factors. These include subtle differences in content, user engagement patterns, sending infrastructure, and even the technical headers of your messages. Let's explore the common reasons behind this disparity and what you can do to ensure all your essential emails reach the inbox.
Understanding the fundamental differences
Even though your transactional and campaign emails might share the same domain and IP address, mailbox providers (like Gmail or Outlook.com) employ sophisticated algorithms that differentiate between types of email based on content, sending patterns, and user interaction. Transactional emails are typically user-initiated, expected, and contain critical information, such as password resets or order confirmations. Campaign emails, on the other hand, are often marketing-related, sent to a broad audience, and may not be explicitly anticipated by every recipient.
The recipient's historical engagement with your domain is a major factor. If recipients consistently open and click your campaign emails, but your transactional test emails are frequently deleted without interaction, mailbox providers may learn to treat the latter differently. This can lead to a divergence in inbox placement, where one email stream performs well while the other is filtered to spam (or the junk folder).
Content is another critical differentiator. Even subtle variations in language, presence of links, images, or even the HTML structure can affect how an email is perceived by spam filters. A slight change in wording or the inclusion of certain keywords in your transactional emails that aren't present in your campaign emails could trigger a spam filter, even if the overall sender reputation is good.
Transactional emails
Triggered by user actions: Sent in response to specific user behavior, such as a purchase, password reset, or account registration. They are usually anticipated.
Purpose: Provide essential information or facilitate an action related to the user's interaction with a service.
Engagement expectation: High open and click rates are expected due to their relevance.
Compliance: Generally exempt from some CAN-SPAM Act requirements, as they are not promotional.
Campaign emails
Marketing or promotional: Sent for marketing, promotional, or informational purposes, often as part of a scheduled campaign.
Purpose: Engage subscribers, drive sales, or provide general updates.
Engagement expectation: Variable open and click rates, depends on content and audience interest.
Compliance: Must comply with regulations like CAN-SPAM (US), CASL (Canada), or GDPR (EU).
Investigating SendGrid's infrastructure and IP reputation
While you might perceive your transactional and campaign emails as coming from the "same IP," it is crucial to understand SendGrid's infrastructure. SendGrid, like many ESPs, uses various IP pools for different types of sending. Your campaign emails might be routed through a highly reputable IP pool specifically maintained for bulk marketing, while your transactional emails might use a different, possibly shared, IP pool. Even if it is a shared IP, the reputation of that specific pool can fluctuate based on the collective sending behavior of all users on it.
Sender reputation is granular, and it is assessed at multiple levels including IP, domain, and even the specific email stream or subdomain. If the transactional email stream has accumulated more complaints or low engagement (perhaps from your testing habits), its individual reputation, or the reputation of the specific IP it uses, could be lower than that of your campaign emails. This can lead to the transactional emails being directed to the spam folder, even with passing authentication.
I often see cases where senders use a single IP for both, but the *nature* of the transactional traffic (e.g., small volumes to many different recipients for password resets) versus large marketing blasts creates different behavioral patterns that mailbox providers detect. Sometimes, a transactional stream might be subject to stricter filtering if it exhibits characteristics associated with malicious activity, even if legitimate, due to its unique sending patterns.
Mailbox providers are incredibly good at "fingerprinting" different sends, even from the same IP or domain. The content of your email plays a significant role. Even if the "code is the same" as you mentioned for your tests, subtle differences in dynamic content, personalization tokens that fail, or even specific keywords can trigger spam filters. Transactional emails, while often simpler, can sometimes contain elements that appear suspicious if not carefully crafted. These elements can include: too many links, overly generic subject lines, or even just unusual formatting.
A common trap for transactional emails is related to testing. If you are sending numerous test emails to your own inbox or a small seed list without proper engagement (opening, clicking, moving to inbox), you might inadvertently be training your mailbox provider that these specific emails are unwanted. Mailbox providers learn from user behavior. If your internal tests are deleted or ignored, it sends negative signals that can impact future delivery of similar emails. It's a tricky cycle to break.
List hygiene is also important, even for transactional sends. Sending to invalid or old email addresses can lead to hitting spam traps. While this is more common with campaign emails, a transactional system pulling from an uncleaned database could also encounter this issue. Hitting spam traps significantly damages sender reputation and can lead to being added to a blacklist (or blocklist).
To prevent issues with transactional emails, it is crucial to ensure they adhere to strict best practices. This includes optimizing subject lines for clarity and relevance, avoiding spammy content, and ensuring a clear call to action.
Best practices for transactional content
Clear subject lines: Make them concise and directly related to the email's purpose.
Relevant content: Focus solely on the information the user expects, avoiding promotional material.
Personalization: Address the recipient by name where appropriate to enhance relevance.
Minimal links: Include only necessary links relevant to the email's transactional nature.
Authentication and technical configuration analysis
Authentication protocols like SPF, DKIM, and DMARC are fundamental for email deliverability. While your emails might be "passing" these checks, subtle misconfigurations or differences in how SendGrid applies them to different sending streams could exist. For instance, the return-path header, also known as the MFrom or Envelope From address, is critical for SPF alignment. If this differs between your transactional and campaign emails, it could impact deliverability, even if your main "From" address is authenticated.
I often advise checking the full email headers of both your successful campaign emails and the transactional emails that land in spam. This can reveal discrepancies in authentication (like a DKIM mismatch or an SPF softfail), routing, or even unexpected headers added by SendGrid or an intermediary. Comparing these headers side-by-side can highlight specific issues. For example, a DMARC verification failed error for transactional emails could indicate an alignment issue not present in your campaigns.
Inspecting email headers for clues
Email headers contain a wealth of information about an email's journey and authentication status. Comparing the headers of a good email to a spam-folder email can pinpoint subtle differences in how they are processed. Key headers to look for include: `Authentication-Results`, `Received-SPF`, `DKIM-Signature`, `Return-Path`, and `X-Mailer`.
Example email header snippetplain
Received: from o1.sg.sendgrid.net (o1.sg.sendgrid.net [167.89.XX.XX])
by mx.google.com with ESMTPS id XXXXX.0
for <recipient@example.com>
(version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256);
Authentication-Results: mx.google.com;
spf=pass (google.com: domain of bounces@sendgrid.net designates 167.89.XX.XX as permitted sender)
smtp.mailfrom=bounces@sendgrid.net;
dkim=pass header.i=@yourdomain.com header.s=sXXXXXX.p;
dmarc=pass (p=none dis=none)
header.from=yourdomain.com
Return-Path: <bounces@sendgrid.net>
From: Your Name <info@yourdomain.com>
Subject: Your Transactional Update
Message-ID: <XXXXXXXX.XXXXXX@sendgrid.com>
Bringing it all together for better deliverability
The key to resolving deliverability disparities between transactional and campaign emails lies in a holistic approach. It is not just about the IP or domain, but the entire context of the email: its content, the recipient's expectedness, their engagement, and the minute technical details in the headers.
By meticulously reviewing each of these areas, you can identify the specific factors causing your transactional emails to be filtered. Often, it comes down to minor differences in content, or how your test sending behavior is inadvertently signaling negative reputation to mailbox providers. Continuous monitoring of your deliverability metrics for both email streams is essential for maintaining optimal inbox placement.
Views from the trenches
Best practices
Monitor reputation across different email streams regularly, differentiating between transactional and campaign performance.
Ensure consistency in branding, authentication, and headers for all email types to build unified sender trust.
Maintain separate IP pools for high-volume marketing and critical transactional sends to isolate reputation risks.
Segment email lists based on engagement and clean inactive contacts to protect sender reputation for transactional emails.
Common pitfalls
Sending large volumes of transactional test emails to inactive or internal addresses, which can negatively impact engagement metrics.
Mixing promotional content within transactional emails, leading to higher spam complaints and filter triggers.
Overlooking subtle differences in email headers or authentication setup between transactional and campaign sending configurations.
Implement a DMARC policy with reporting to gain visibility into authentication failures and email routing.
Regularly check your domains and IPs against major email blocklists (or blacklists), even if you think your deliverability is good.
Use email deliverability testing tools to analyze transactional email content for potential spam triggers before sending.
Segment your audience for transactional emails by behavior and engagement to ensure higher relevance and lower complaint rates.
Marketer view
Marketer from Email Geeks says that deliverability issues, where transactional emails go to spam while campaign emails go to the inbox, often stem from content differences, as email filters analyze many data points.
2023-12-02 - Email Geeks
Marketer view
Marketer from Email Geeks states that if you are sending many test transactional emails to yourself without engaging with them, you might be training your own inbox or the mailbox provider to mark them as spam. They recommend checking the performance of these email types within SendGrid.
SendGrid consistently land in the spam folder, yet your campaign emails, seemingly from the same sender and IP, arrive in the inbox. This scenario often suggests a deeper nuance in how mailbox providers assess different email types and how your email service provider (ESP) handles them. It is not always as straightforward as checking the IP or domain name alone.
Gmail or 
Outlook.com) employ sophisticated algorithms that differentiate between types of email based on content, sending patterns, and user interaction. Transactional emails are typically user-initiated, expected, and contain critical information, such as password resets or order confirmations. Campaign emails, on the other hand, are often marketing-related, sent to a broad audience, and may not be explicitly anticipated by every recipient.
