How To Troubleshoot Delivery Delays in Exchange Online

In this post we are going to walk through how to troubleshoot delivery delays in Exchange Online. If users are not receiving emails or are receiving delayed emails, this guide will help you resolve this problem. This post makes up part of my full MS-220 exam study guide.

Determine if the issue is with the client or server

It is important to know when you begin to look at email delivery issues, whether this is an issue with the client side application or the mail server. We can determine this in a couple of ways depending on how the issue is reported to us. 

Client Issues

If a user or multiple users report that they are not receiving email to their Outlook desktop client, they can check Outlook on the web. If the email is available on the web, this is likely a client side issue.

Server Issues

If multiple users are affected and some emails are not visible in the Outlook desktop client or on the Outlook Web App, then it is likely a server side issue.

Troubleshooting Outlook client issues

In the event you are experiencing issues with the Outlook desktop client there are some steps you can take to resolve or repair the issues. In some instances client site issues can occur due to the following: corrupt profiles, corrupt office installation, bugs in recent updates. 

Try the following in this order:

Change Outlook cached mode to online mode:

  1. From within Outlook click File > Account settings > Account settings
  2. Select your primary email and click Change
  3. Uncheck the box next to ‘use cached Exchange mode’
  4. Restart Outlook. 

Re-create Outlook Profile:

  1. From the Windows start menu, open Control Panel
  2. Change ‘view by’ to small icons in the top right
  3. Select Mail > Show Profile > Add
Repair Office installation:
  1. From the Windows start menu open Control Panel
  2. Select Uninstall a program
  3. Select Office from the programs list and click Change
  4. Select Online repair and click Repair
Roll back to previous version of Office
  1.  Open Command Prompt as an administrator
  2. 3. Use the following link to find the version of Office you require: here.
  3. Run the following command with your required version of office
"C:\Program Files\Common Files\microsoft shared\ClickToRun\officec2rclient.exe" /update user updatetoversion=16.0.xxxx.yyyy

Troubleshoot Exchange Online server issues

Check the Exchange Online service health

The Microsoft Service Health Dashboard provides information on current and past services issues with Microsoft 365 services. In this instance we specifically want to look at the Exchange Online service health. To check the health status of Exchange Online, do the following:

1. Login to the Microsoft 365 Admin Centre:

2. From the left hand menu, select Health > Service Health

3. Use the Overview and Issue history tab to view current and previous service issues.

Check for mail flow issues

If not a service issue with Exchange Online, there is a chance the issue is being caused by either bad configuration, or a 3rd party service. It is important to check how your mail is being routed and which rules it is being affected by. 

Firstly you should check what your public mail server (MX) record is. When email is sent to your domain, its first stop is to the mail server that is advertised publicly. You can check this by using the nslookup command in PowerShell as follows. 

nslookup  -querytype=mx

In some instances, this record would be a 3rd party mail service such as a filter or security platform. If so, you can check the service health of that specific service or you can check the timestamps of when the email was sent, when the public mail service received the email and when the email was delivered to your mail server and client.

If your message was sent internally or you have determined the issue is not be caused by a 3rd party service, then you should look at how your mail is being affected by rules or internal issues. 


Thank you for taking the time to read my post on how to troubleshoot delivery delays in Exchange online. In this post we covered how to identify if you are experiencing a server or client side problem, as well as how to resolve the issues.

Daniel Bradley

My name is Daniel Bradley and I work with Microsoft 365 and Azure as an Engineer and Consultant. I enjoy writing technical content for you and engaging with the community. All opinions are my own.

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