gmail.com rejects our 365 emails

Hi @Ruba AbuArqoob,

I hope you're having a great day. I can understand how inconvenient it can be when emails sent from Microsoft 365 are rejected by gmail.com, particularly when this has been occurring for an extended period.

When Gmail blocks a message and indicates that it’s suspected as spam, this typically points to an issue with email authentication, sender reputation, or message content, rather than a problem with Outlook on the web itself.

To help narrow this down, I recommend reviewing the following common causes and steps:

1/ Review the rejection (NDR) message:

First, please check the bounce‑back or Non‑Delivery Report (NDR) you receive. Gmail usually includes a specific error code or link in this message, which can help determine whether the rejection is related to spam filtering, authentication issues, or sender reputation.

2/ Verify email authentication:

Even when messages are legitimate, Gmail applies very strict authentication requirements.

If possible, please ask your IT administrator (with admin access) to confirm that your domain is correctly configured with the following records:

• SPF (Sender Policy Framework)
• DKIM (DomainKeys Identified Mail)
• DMARC

Missing or incorrectly configured records are among the most common reasons Gmail rejects emails. These settings can be reviewed and updated through the Microsoft 365 Admin Center. More details are available here: Email authentication in cloud organizations.

3/ Review Google’s sender requirements:

If your organization sends a higher volume of emails to Gmail recipients, it’s also important to review Google’s sender guidelines. Even if you’re not considered a bulk sender, meeting these requirements can significantly improve deliverability.

You can review the guidelines here: Email sender guidelines FAQ.
This is a non-Microsoft website. The page appears to be providing accurate, safe information. Watch out for ads on the site that may advertise products frequently classified as a PUP (Potentially Unwanted Products). Thoroughly research any product advertised on the site before you decide to download and install it. 

In addition, testing by sending a simple email (plain text only, with no links or attachments) can help determine whether message content is contributing to the issue.

4/ Use Google Postmaster Tools:

If this has been an ongoing problem, registering your domain with Google Postmaster Tools can provide valuable insights into how Gmail views your sender reputation and why emails may be blocked.

5/ Review sender reputation using message trace:

If you’re using a custom domain, please note that Microsoft 365 sends email from shared IP addresses, which Microsoft manages. However, your IT administrator can still run a Message Trace in the Microsoft 365 Admin Center to confirm that messages are being sent successfully and are only being rejected by Gmail.

This article outlines the steps: Message trace in the new Exchange admin center in Exchange Online.

6/ Contact Gmail and Microsoft Support if needed:

• If the rejection message includes a delisting or appeal link, I recommend following that process directly with Gmail.
• If authentication is correctly set up and rejections continue, Microsoft Support can help review sending patterns and logs. Your IT administrator can create a support ticket by signing in to the Microsoft 365 admin center and following the steps in this link: Get support for Microsoft 365 for business to create a support ticket from the admin center or by calling phone support to contact Microsoft Support: Customer service phone numbers. If needed, this article may also help you identify your Microsoft 365 administrator: How do I find my Microsoft 365 admin?.

Note: As an Independent Advisor, while I can help with general guidance and common troubleshooting from this forum, no one here has access to Microsoft’s internal systems or administrative tools for account‑specific or backend matters. Nevertheless, I’m glad to continue assisting and help guide you toward the next steps.

I hope this helps clarify the situation and move things forward. Please feel free to share any updates or let me know if you need further assistance. I’ll be glad to help.

I look forward to your reply.

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Gmail is rejecting messages because they’re being classified as spam based on the reputation and characteristics of the mail coming from Microsoft 365.

Key points and actions:

1. Understand how Microsoft 365 sends mail
   • Outbound IPs from Microsoft 365 have forward-confirmed reverse DNS (PTR and A records match) and use outbound.protection.outlook.com in HELO/EHLO.
   • Example from the service:
     • IP: 157.56.110.65
     • PTR: 157.56.110.65 = mail-bn1on0065.outbound.protection.outlook.com
     • A: mail-bn1on0065.outbound.protection.outlook.com = 157.56.110.65
   • Gmail will see this pattern and use it, together with content and reputation, to decide if mail is spam.
2. Check that the sending path is correct
   • If mail is going out directly from Microsoft 365, ensure that:
     • The domain’s MX records point where intended (ideally to Microsoft if using Microsoft 365 as primary service).
     • No intermediate smart host or device is altering headers in a way that makes messages look suspicious.
   • If a non-Microsoft outbound provider is used, configure Microsoft 365 to route outbound mail via that smart host as documented, and ensure that provider is correctly set up and reputable.
3. Verify that the organization is not advertising non-routable IPs
   • Gmail and Microsoft 365 can reject connections that appear to come from non-internet-routable IP ranges (for example 10.x.x.x, 192.168.x.x, 172.16–31.x.x).
   • Ensure any on-premises or relay servers that touch outbound mail are not presenting private IPs in HELO/EHLO or reverse DNS.
4. Reduce spam-like characteristics
   • Review content and sending patterns that might cause spam classification (bulk marketing style, misleading subjects, URL-heavy content, etc.).
   • Ensure users are not sending unsolicited bulk mail from the tenant, which can damage reputation and cause Gmail to reject.
5. Use Microsoft 365 anti-spam controls correctly
   • Microsoft 365 already classifies outbound messages and may route suspected spam through the high-risk delivery pool or NDR them.
   • If Gmail is rejecting, it indicates reputation/content issues at the destination; improving sending practices and reputation is required.
6. Work with recipients and error details
   • Ask Gmail recipients to provide the full NDR text and message headers.
   • Use the NDR code and explanation to see exactly why Gmail rejected the message and adjust sending behavior accordingly.

If the organization routes inbound mail through another provider or appliance before Microsoft 365, ensure that configuration is correct and that any mail flow rules or connectors are not causing the messages to look suspicious to Gmail.

References:

• Recipient rejects mail from Microsoft 365 and host name does not match IP address error
• Frequently asked questions - Anti-spam protection
• Anti-spam protection in cloud organizations
• What's the difference between junk email and bulk email in cloud organizations?
• External senders - Troubleshoot email sent to Microsoft 365
• Emails sent from Microsoft 365 in a hybrid deployment are rejected and nondelivery reports are received