Emails from Outlook to Gmail takes hours to 1 day to be received

Question

Hi all,

I have an issue with my Outlook account. I'm using Microsoft 365 Apps for business.

I already reported this issue in the past (in 2023) but it never got properly solved.

When I send an email from my outlook account to my gmail account, I receive it with a huge delay. Sometimes hours or even 1 day delay This happens when I have multiple attachments to the email.

When I don't send it with attachments, I don't have the issue.

I did the test via Outlook app and via web version.

The thing is that I'm working with differents clients, with different email accounts, and sometimes we need to share the info urgently. I cannot wait 1 day or even hours.

When I acquired the subscription back in 2019, I did not experience this issue. But, if I remember correctly, this started in 2023.

Has anyone encountered the same issue and found the solution?

Thank you,

Answer 1

Hi @Mouhcine

To better address your issue, could you provide additional information for the following questions: 

Since the affected mailbox is a business account, may I ask does this behavior occur with other user accounts as well, or only with your specific account? 

Does the delay occur only when sending emails to Gmail recipients, or have you also observed the same behavior when sending to other email providers? 

Based on my research, this behavior might be related to Gmail’s security and email‑handling policies for messages sent from enterprise email systems. According to Google’s official documentation, emails sent to Gmail, especially those containing attachments, may be subject to additional security checks and processing before they are delivered to the Inbox. 

To help improve email delivery reliability and reduce potential delays, I strongly recommend setting up email authentication for your domain, including SPF, DKIM, and DMARC. 

Major email providers such as Gmail have implemented stricter security and filtering policies, particularly for emails sent from business or enterprise mail platforms. Messages that are not fully authenticated may still be delivered; however, they are more likely to be delayed, rate‑limited, or routed to spam, especially when attachments are included. 

Properly configuring email authentication enables receiving mail systems to: 

Verify that emails are legitimately sent on behalf of your domain. 

Confirm that message content has not been modified during transmission.

Build a stronger and more trustworthy sending reputation for your domain over time. 

While email authentication cannot completely eliminate all delivery delays, since Gmail may still perform in‑depth security scans on attachments, it is now considered a best practice and, in many cases, a minimum requirement for reliable email delivery to Gmail and other major email providers. 

For this reason, I recommend working with your current email administrator to ensure that SPF, DKIM, and DMARC are properly configured, which will help optimize deliverability and reduce the risk of delayed or filtered emails. 

You can refer more via:  

Authenticate Outbound Email to Improve Deliverability | Microsoft Community Hub 

Email sender guidelines - Google Workspace Admin Help 

Note: This information is provided as a convenience to you. These sites are not controlled by Microsoft, and Microsoft cannot make any representations regarding the quality, safety, or suitability of any software or information found there. Please ensure that you fully understand the risks before using any suggestions from the above link. 

Please understand that our initial reply may not always immediately resolve the issue. However, with your help and more detailed information, we can work together to find a solution. 

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Answer 2

The size of the attachments were 2 MB