Why are my SendGrid transactional emails not appearing in Outlook inboxes?
Michael Ko
Co-founder & CEO, Suped
Published 17 Jul 2025
Updated 19 Aug 2025
8 min read
It can be incredibly frustrating when your SendGrid transactional emails show as 'delivered' but never actually appear in the recipient's Outlook inbox. This is a common scenario, especially with Microsoft's aggressive filtering mechanisms. The term 'delivered' from your email service provider simply means the email was accepted by the recipient's mail server, not necessarily that it landed in the inbox.
Microsoft, including Outlook.com, Hotmail, and Office 365, employs sophisticated filtering. This can result in legitimate emails being silently dropped, routed to the junk folder, or completely disappearing from view, even when your sending platform indicates successful delivery. Understanding why this happens is crucial for improving your transactional email deliverability.
This guide will explore the primary reasons why your transactional emails from SendGrid might not be appearing in Outlook inboxes and provide actionable steps to diagnose and resolve these issues. We will delve into common deliverability challenges and offer practical advice to ensure your important messages reach their intended recipients.
Understanding the 'delivered' status
The distinction between an email being 'delivered' and it reaching the 'inbox' is often misunderstood. When SendGrid reports an email as delivered, it means their servers successfully handed off the email to the recipient's mail server, such as Microsoft's. However, what happens after that handoff is entirely up to the receiving server and its filtering rules. This is where the 'ghosting' effect often occurs, where an email is accepted but never seen by the user.
Microsoft's filtering system is highly sensitive to sender reputation, content, and recipient engagement. If any of these factors are flagged, your emails might not make it to the primary inbox. It is a nuanced process, and even minor issues can lead to significant deliverability problems. Transactional emails, despite their importance, are not immune to these filters.
One common issue is when email providers (like Microsoft) accept the email but silently filter it to a junk folder, or even drop it entirely, without generating a bounce notification back to the sender. This can be especially frustrating because SendGrid will report delivery, making diagnosis difficult. This typically indicates a soft block or a reputation-based filtering decision on the recipient's side.
This can happen even if other emails from the same dedicated IP and sender address are delivering without issue to the same domain. This points to a specific characteristic of the problematic email stream, such as its content or the specific recipient's internal rules.
Common causes of Outlook filtering
Several factors can contribute to your SendGrid transactional emails being filtered or blocked by Outlook. The most prominent factor is your sender reputation, which Microsoft heavily weighs. If you are using shared IPs with SendGrid, your deliverability can be impacted by the sending practices of other users on those IPs. Poor sending behavior from others can lead to the shared IP being placed on a blacklist or blocklist, affecting all senders using it.
Content is another critical element. Even for transactional emails, spammy keywords, broken links, disproportionate image-to-text ratios, or hidden text can trigger spam filters. Microsoft's algorithms are adept at identifying suspicious patterns, even in seemingly benign messages. For instance, an email containing an unusual link or a suspicious attachment might be flagged.
Lack of recipient engagement also plays a significant role. If recipients frequently delete your emails without opening them, move them to junk, or simply ignore them, this sends a negative signal to Outlook's filters. Unlike marketing emails, transactional emails often have a clear call to action or important information, so a lack of engagement suggests a problem. Moreover, individual recipients might have local transport rules set up in their Outlook accounts that redirect specific types of emails or sender domains.
Authentication and IP reputation
Proper email authentication is non-negotiable for deliverability, especially to Microsoft inboxes. SPF, DKIM, and DMARC records verify that your emails are legitimately coming from your domain and help prevent spoofing and phishing. Microsoft heavily relies on these protocols to determine email legitimacy.
Ensure your SPF record is correctly configured to include SendGrid's sending IPs, and your DKIM records are properly signed. A strong DMARC policy (p=quarantine or p=reject) tells receiving servers how to handle emails that fail SPF or DKIM checks, further enhancing your domain's reputation. Incorrect or missing DMARC records can severely impact your deliverability to Outlook.
Even with perfect authentication, your sending IP's reputation is paramount. If your SendGrid IP (especially shared IPs) has been used by other senders for malicious or low-quality emails, it might land on a public or private email blacklist or blocklist. Microsoft (and other major mailbox providers) use these lists to filter incoming mail, so checking your IP's status on various blocklists is a proactive measure. You can usually check the status of your IP on the SendGrid activity feed.
Checking your SendGrid IP reputation
Monitoring your IP reputation is a proactive step. While SendGrid manages its shared IP reputation, a dedicated IP gives you more control. Microsoft offers specific programs like the Smart Network Data Services (SNDS) and Junk Mail Reporting Program (JMRP) that provide insights into how Microsoft views your sending practices. Registering for these programs can offer valuable feedback on your deliverability to Outlook. It is important to remember that improving a poor sender reputation takes time and consistent good sending practices.
Best practices for SendGrid senders
To maximize your chances of inboxing with Outlook, adopt a comprehensive approach to email deliverability. Start by ensuring all your email authentication records (SPF, DKIM, DMARC) are correctly set up and aligned with your sending domain. This foundational step is critical for building trust with mailbox providers.
Next, focus on your content. Even for transactional emails, avoid anything that might appear spammy. Keep your HTML clean, minimize excessive images, and ensure all links are clear and functional. If your emails include links, make sure they are to trusted domains and not shortened URLs that can be perceived as suspicious. Consistent email volume and avoiding sudden spikes can also help maintain a good reputation.
Regularly monitor your SendGrid activity logs for any bounce or drop events, even if they show as 'delivered.' Pay close attention to unique recipient domains or specific emails that consistently fail to appear in inboxes. This could indicate localized filtering rules or unique issues with those particular recipients. Consider implementing email address validation at the point of collection to minimize sending to invalid or dormant addresses, which can negatively impact your sender reputation.
Finally, encourage positive recipient engagement. For transactional emails, this might mean clear subject lines that indicate the email's purpose, ensuring the content is valuable and relevant, and making it easy for users to find the information they need. If recipients consistently engage with your transactional emails, this signals to mailbox providers that your mail is wanted and trustworthy. Following these best practices can significantly improve your deliverability to Microsoft inboxes and beyond.
Views from the trenches
Best practices
Maintain a healthy sender reputation by consistently sending valuable and expected emails, even for transactional communications.
Implement and monitor email authentication protocols like SPF, DKIM, and DMARC for your sending domain.
Regularly clean your email lists to remove inactive or invalid addresses, reducing bounce rates and improving engagement.
Design transactional emails with clear content, concise subject lines, and minimal spam triggers to ensure they are easily recognized and valued by recipients.
Common pitfalls
Relying solely on 'delivered' status in SendGrid without investigating actual inbox placement or spam folder delivery.
Ignoring recipient engagement signals, such as low open rates or frequent deletions, which can negatively impact sender reputation.
Failing to monitor your sending IP and domain for blocklist (or blacklist) placements, especially when using shared IPs.
Overlooking specific content elements or formatting issues that might trigger Microsoft's spam filters for transactional emails.
Expert tips
Monitor Microsoft's Smart Network Data Services (SNDS) to gain insights into how your mail is perceived by Outlook and Hotmail filters.
Consider using a dedicated IP address with SendGrid if your transactional email volume is high, to have more control over your sending reputation.
Encourage recipients to add your sending address to their safe senders list or address book to improve future deliverability.
Regularly test your transactional emails across various email clients, including different versions of Outlook, to catch rendering or filtering issues early.
Expert view
Expert from Email Geeks says Microsoft often uses a 'ghosting' action for higher-risk mailers, like inactivity notices, where emails are delivered but not seen. Changing the subject line or body content might offer a temporary fix, but underlying reputation issues related to unqualified prospects or bot sign-ups need to be addressed.
January 22, 2021 - Email Geeks
Expert view
Expert from Email Geeks says if the issue is verified to be occurring with only a single recipient domain, it suggests that local transport rules or specific inbox configurations are likely responsible for the emails not appearing.
January 22, 2021 - Email Geeks
Improving your transactional email deliverability
When your SendGrid transactional emails aren't appearing in Outlook inboxes, the solution often involves a multi-faceted approach. It is crucial to move beyond simply checking the 'delivered' status and delve deeper into sender reputation, email authentication, content quality, and recipient engagement. By diligently implementing best practices, monitoring your sending metrics, and proactively addressing any red flags, you can significantly improve your transactional email deliverability to Microsoft inboxes.
Remember, consistent effort and attention to detail are key in the ever-evolving landscape of email deliverability. Staying informed about changes in mailbox provider policies, such as Outlook's new sender requirements, will help ensure your critical transactional emails reach their intended audience reliably.
Outlook.com, Hotmail, and Office 365, employs sophisticated filtering. This can result in legitimate emails being silently dropped, routed to the junk folder, or completely disappearing from view, even when your sending platform indicates successful delivery. Understanding why this happens is crucial for improving your transactional email deliverability.
SendGrid activity feed.
Smart Network Data Services (SNDS) and Junk Mail Reporting Program (JMRP) that provide insights into how Microsoft views your sending practices. Registering for these programs can offer valuable feedback on your deliverability to Outlook. It is important to remember that improving a poor sender reputation takes time and consistent good sending practices.
