How to Fix Microsoft 365 Email Delivery Delays to Gmail
Question details
Users are experiencing significant delays, ranging from 15 minutes to 12 hours, when sending emails from Microsoft 365 to Gmail addresses, often accompanied by temporary delivery failure errors.
- Product
- Microsoft 365
- Device & OS
- not provided
- Scenario
- Sending standard emails or emails with attachments from a Microsoft 365 account to external Gmail recipients.
- Observed behavior
- Emails leave the Outbox and appear as sent, but users receive temporary delivery error notifications, and the messages take hours to finally reach the Gmail recipients' inboxes.
Ensure you have Microsoft 365 administrator credentials, as you will need access to the Exchange admin center to perform a message trace.
Run a Message Trace in Exchange Online
Using the message trace tool in the Exchange admin center helps pinpoint exactly where the email is getting stuck between Microsoft 365 and Gmail.
A message trace follows email messages as they travel through your Exchange Online organization. It can reveal if a message was deferred, rejected, or delayed by Microsoft servers or by Gmail's receiving servers.
Sign in to the Microsoft 365 admin center with your administrator account, click 'Show all' in the left navigation menu, and select 'Exchange'.
In the Exchange admin center, navigate to the 'Mail flow' section on the left sidebar and click on 'Message trace'.
Click 'Start a trace'. Enter the sender's Microsoft 365 email address and the recipient's Gmail address. Set the time range to cover when the delayed email was sent.
Click 'Search' and review the delivery status. Look for 'Deferred' or 'Failed' statuses and click on the specific message to view detailed error codes and routing delays.
Verify Message Size and Remove Large Attachments
Emails that exceed standard size limits can be temporarily throttled or delayed by Gmail's incoming mail servers.
Gather Message Headers for Microsoft Support
If emails continue to be delayed, you need to collect raw message headers so Microsoft Support can investigate server-side routing issues.
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Frequently Asked Questions
Why do emails from Microsoft 365 to Gmail take hours to deliver?
Delays are often caused by temporary server throttling, strict anti-spam filtering on Gmail's side, large attachments taking time to process, or missing DNS authentication records like SPF, DKIM, and DMARC.
What does 'message could not be delivered' mean if the email eventually sends?
This usually indicates a temporary delivery failure (a 400-level SMTP error). The Microsoft 365 server could not immediately hand the message over to the Gmail server, so it temporarily deferred the message and kept retrying until successful.
How can I prevent my emails to Gmail from being delayed in the future?
Ensure your custom domain's SPF, DKIM, and DMARC records are correctly published in your DNS settings. This helps Gmail quickly verify your sender identity, bypassing many spam filters that cause delays.
Are there size limits for sending emails from Microsoft 365 to Gmail?
Yes. While Microsoft 365 can be configured to send larger emails, Gmail limits incoming messages to a maximum of 50 MB. Exceeding this limit will cause the email to be rejected, and approaching it may cause scanning delays.
