How to fix Gsuite sender reputation issues when business emails are sent to quarantine in Outlook?
Michael Ko
Co-founder & CEO, Suped
Published 2 Jun 2025
Updated 16 Aug 2025
6 min read
Dealing with business emails from G Suite being quarantined in Outlook can be a frustrating experience. It often points to underlying sender reputation issues, even if you are only sending one-to-one communications. This problem means your important messages are not reaching their intended recipients' inboxes, disrupting workflows and communication channels.
When emails from your Google Workspace (G Suite) account are flagged and sent to quarantine (or junk/spam folders) by Microsoft's email systems, it indicates that Outlook perceives your sending domain or IP address as suspicious or potentially malicious. This guide will walk you through the steps to diagnose and resolve these issues, helping you restore your sender reputation and ensure your emails reach the inbox.
The basics of sender reputation and email quarantine
Sender reputation is essentially a trust score assigned to your sending domain and IP address by mailbox providers. A low score can lead to your emails being quarantined, rejected, or sent directly to spam folders. Microsoft, like other major email providers, uses sophisticated algorithms to assess this reputation. Factors contributing to a low reputation can include high spam complaints, sending to invalid email addresses, or a lack of proper email authentication.
When Outlook quarantines an email, it means the message is held in a special folder rather than delivered to the recipient's inbox or junk folder directly. Administrators can review these messages and decide whether to release them, deny delivery, or delete them. This acts as a protective measure against perceived threats, but it also impacts legitimate business communications. You can learn more about managing quarantined messages in Google Workspace.
The challenge is that reputation is dynamic. A sudden change, such as a bulk send, or even a perceived spoofing event, can quickly diminish your standing. Even if you're primarily sending one-to-one emails, a historical issue or a current anomaly could trigger quarantine filters.
How email quarantining works
Email quarantine is a security measure implemented by email service providers, like Outlook. Instead of delivering suspicious emails directly to a user's inbox or junk folder, they are held in a secure, isolated area. This allows administrators to review messages flagged as potential spam, phishing attempts, or malware before they reach end-users. It's a critical layer of defense, but sometimes legitimate emails can be caught in the filters.
Identifying the root causes
The first step in fixing the problem is understanding why your emails are being quarantined. Start by checking your domain's health. You should be using Google Postmaster Tools to monitor your domain's reputation with Google. While this doesn't directly show Outlook's view, it provides a general health indicator. A low IP reputation could also be a factor.
Next, confirm your email authentication records are correctly set up. SPF, DKIM, and DMARC are crucial for proving your emails are legitimate. An improperly configured DKIM, for instance, can be a root cause for delivery issues, as it makes your emails appear unverified. Use a DNS checker to verify these records for your domain.
Consider your sending patterns. Even if current emails are one-to-one, past bulk sends (especially if they had low engagement or high bounce rates) can negatively impact your reputation. If your issue started recently, it's vital to look at any changes in your email sending practices around that time. There's also the possibility of domain spoofing, where malicious actors send emails pretending to be from your domain, which can severely damage your reputation without your direct knowledge.
Missing or incorrect records lead to flags and quarantine.
Sending volume
Gradual, consistent increases in volume are acceptable.
Sudden, large spikes often trigger spam filters.
Recipient engagement
High open rates and clicks demonstrate good content.
Low open rates, high bounce rates, and spam complaints harm reputation.
Content quality
Relevant, personalized emails are well-received.
Spammy keywords or broken links lead to filtering.
Essential technical configurations for deliverability
Implementing strong email authentication is paramount. For G Suite, this means ensuring your SPF, DKIM, and DMARC records are correctly published in your DNS. SPF (Sender Policy Framework) specifies which IP addresses are authorized to send emails on behalf of your domain. DKIM (DomainKeys Identified Mail) provides a digital signature, allowing recipients to verify the email's authenticity and integrity. DMARC (Domain-based Message Authentication, Reporting, and Conformance) builds on SPF and DKIM, telling recipient servers how to handle emails that fail authentication and providing reporting on these failures.
If you've recently set up or corrected your DKIM records, understand that it can take time for these changes to propagate across the internet and for inbox providers like Outlook to re-evaluate your domain's reputation. Patience is key, but consistent monitoring is also required. You can use a DMARC record generator to ensure your policy is correctly formatted.
Invalid DKIM signature: Emails appear tampered with or unsigned.
No DMARC policy: No instructions for handling unauthenticated emails, leading to default spam filtering.
Impact
Emails are more likely to be marked as spam or quarantined due to lack of verifiable authenticity.
Correct configuration
Complete SPF record: Includes all legitimate sending sources.
Valid DKIM signature: Matches the domain and sender.
DMARC policy (p=quarantine/reject): Instructs how to handle unauthenticated emails and provides reporting.
Impact
Increased trust, improved deliverability, and protection against spoofing.
Additionally, if you have contacts in Office 365, asking them to whitelist your domain or email address can bypass many quarantine filters. This is a short-term fix but can be useful for critical communications while you address the root cause. You can also review Microsoft's guidelines on allowing and blocking lists.
Enforcing DMARC protection
Once your SPF and DKIM records are correctly configured and showing consistent passing rates, consider moving your DMARC policy to an enforcement mode (p=quarantine or p=reject). This will tell recipient servers, including Outlook, to quarantine or reject emails that fail authentication. While seemingly aggressive, this policy significantly enhances your domain's credibility and protects against spoofing, which in turn can lead to better inbox placement over time.
Maintaining a healthy sender reputation
Maintaining a healthy sender reputation is an ongoing process. Regularly monitor your email domain reputation using Postmaster Tools and DMARC reports. These tools provide insights into your email delivery performance, including spam complaints, IP reputation, and authentication errors, helping you catch issues early.
Beyond technical configurations, content quality and list hygiene are critical. Ensure your emails provide value to recipients and avoid spammy keywords or excessive links. Regularly clean your email lists to remove inactive or invalid addresses, as sending to non-existent users can negatively impact your sender score. For further reading, check Google's email sender guidelines.
Avoiding spam traps
Spam traps are email addresses specifically designed to catch spammers. Sending to a spam trap can severely damage your sender reputation, leading to immediate blocklisting (or blacklisting). To avoid them, implement strict list hygiene practices, never purchase email lists, and regularly remove inactive subscribers. Regularly checking blocklists is a good practice.
Common scenarios and considerations
A common issue is when a domain with a good reputation starts experiencing quarantine problems suddenly. This might occur after a migration to Office 365 or if emails sent to Microsoft domains are being sent to junk.
Sometimes, emails from Gsuite are rejected by the G Suite server itself, or an external platform like Zoho. If you're using a third-party service for some sends, ensure its configuration aligns with your domain's authentication settings.
Views from the trenches
Best practices
Always maintain accurate SPF, DKIM, and DMARC records for your sending domains.
Monitor your sender reputation regularly using Google Postmaster Tools and DMARC reports.
Segment your email lists and send targeted content to improve recipient engagement.
Implement a strict list hygiene process to remove inactive and invalid email addresses.
Common pitfalls
Ignoring DMARC reports, which contain critical insights into authentication failures.
Sending to outdated or unverified email lists, leading to high bounce rates and spam complaints.
Experiencing sudden spikes in email volume that can trigger spam filters.
Failing to enforce DMARC (moving from p=none to p=quarantine or p=reject) over time.
Expert tips
Focus on consistent email authentication and monitoring, as reputation recovery takes time.
Investigate any sudden changes in email deliverability, as they often point to a recent trigger.
Implement feedback loops where available to quickly identify and address spam complaints.
Engage with your recipients to foster positive interactions like opens and replies.
Expert view
Expert from Email Geeks says to confirm that the client is not sending spam, even if it's mostly one-to-one communication, as past bulk sends can have lingering effects.
2021-07-08 - Email Geeks
Marketer view
Marketer from Email Geeks says they started seeing their issues about a week ago, indicating a recent change or trigger that needs to be identified.
2021-07-08 - Email Geeks
Restoring trust and ensuring inbox delivery
Fixing G Suite sender reputation issues with Outlook quarantine requires a multi-faceted approach. It involves a deep dive into your email authentication, consistent monitoring, and adherence to best practices for email sending. Remember that reputation takes time to build and rebuild, so persistence is key.
By prioritizing proper technical setup, engaging with your audience, and staying vigilant against potential threats like spoofing, you can significantly improve your deliverability and ensure your business emails consistently reach their intended inboxes.
Outlook can be a frustrating experience. It often points to underlying sender reputation issues, even if you are only sending one-to-one communications. This problem means your important messages are not reaching their intended recipients' inboxes, disrupting workflows and communication channels.
Google Workspace (G Suite) account are flagged and sent to quarantine (or junk/spam folders) by Microsoft's email systems, it indicates that Outlook perceives your sending domain or IP address as suspicious or potentially malicious. This guide will walk you through the steps to diagnose and resolve these issues, helping you restore your sender reputation and ensure your emails reach the inbox.
Outlook. Instead of delivering suspicious emails directly to a user's inbox or junk folder, they are held in a secure, isolated area. This allows administrators to review messages flagged as potential spam, phishing attempts, or malware before they reach end-users. It's a critical layer of defense, but sometimes legitimate emails can be caught in the filters.
G Suite, this means ensuring your SPF, DKIM, and DMARC records are correctly published in your DNS. SPF (Sender Policy Framework) specifies which IP addresses are authorized to send emails on behalf of your domain. DKIM (DomainKeys Identified Mail) provides a digital signature, allowing recipients to verify the email's authenticity and integrity. DMARC (Domain-based Message Authentication, Reporting, and Conformance) builds on SPF and DKIM, telling recipient servers how to handle emails that fail authentication and providing reporting on these failures.
Office 365, asking them to whitelist your domain or email address can bypass many quarantine filters. This is a short-term fix but can be useful for critical communications while you address the root cause. You can also review Microsoft's guidelines on allowing and blocking lists.
