Why Office365 Is Running Slow

It is common for Office 365 to run slow and in this document I will talk about this and what to do about it.

Table of Contents


There are several reasons Office365 can start running slow. These can be:

  • Internet connection

  • Software problems

  • Hardware issues

  • Add-ons

  • File sync

Internet connection

The first requirement is the most important. You must have a solid connection to the web. This means it must have a high bandwidth and low latency. The reasons for this are because you are working in a browser to use your applications. You should also know that you can have a fast connection but still have problems. For example, if your latency is high, you will still experience problems. I encountered this at my last job. They were on an all wireless infrastructure and had a fast connection. Users still had many issues with delays in Office365 which management did not understand. This is because low latency is just as important as a quick download speed.

To fix internet connection issues, start with the routers and firewalls. These are often culprits and overlooked. Make sure applications have complete access. Firewalls will block things because they see your applications as threats. Many people do not know how to configure firewalls either which is another issue. You will need to specifically check IP addresses, protocols, and file types. 

Always opt for a wired connection unless you have no choice. Hopefully, that will never be the case. Wireless connections should only be for minor applications like checking email and browsing the web. Please don’t make your applications work on wireless, they will not do so reliably. 

Software Problems

These types of issues revolve around outdated software, but malware causes many issues too. Keep your machine updated. This means the operating system and the applications. Too often I see people just let their machines do operating system updates and do not delve any further. If you are on windows, the optional updates almost always need to be done. Pay attention to them. Your applications also need updates. Applications are usually neglected. The last two places I worked, applications like browsers were ignored. There is no reason for this. 

Another thing you need to do or have done is to remove startup programs from your settings. These really affect your machine. They will start up in the background and consume resources while doing nothing at all. There can be 10-20 programs doing this. Many, like Adobe or Microsoft products, consume vast amounts of resources. 

Close your unused applications. You do not need to keep them going, just in case. The same goes for browser tabs. You should close everything except Office365 applications. This is the best way to improve your machine’s performance. The last thing I want to mention is to disable Windows telemetry. Everyone should do this. It does not serve a purpose for you and also consumes resources. 

Hardware Issues

This is more rare but can cause a lot of weird issues. Drives are the most important piece of hardware to improve your machine’s performance. A plain SSD is the minimum today that you should consider. A technician should do diagnostics on the drive to check it if your machine is having issues. It could be a variety of issues, so don’t think curing one issue will fix everything. 

Memory can cause issues. Specifically, the lack of it. You want a minimum of 8 GB, but 16 GB is better. Memory can also run slow. A test should be done on memory any time there are machine issues.


Add-ons are special extensions to the app you are using. You can download them for any Office365 application or browser. These can have various effects and can range from slowing your application down to being malware. I would be careful using anything like this and you should have a genuine need to use these.

Macros are in this same category. They can be very nice but also contain malware that will get you hacked. It is because macros are <.vba> code and people will use this to install malware on your system. It has happened to many high-profile companies in the past. So, be wary please. 

File sync

OneDrive syncs your files constantly. This is a big slowdown for your machine. I have seen it many times. It will affect your CPU or memory and cause a lot of lagging in your system. The best thing to do is pause all syncing until you need it. It is a real pain otherwise. 

Specific Outlook Solutions

When Outlook is running slow and you have ruled out the previous issues, it is time to look at the folders. There can be too many items being stored in your email folders. This will cause a slowdown. Go through them and delete what you can. 

Make sure Office365 is not keeping files forever. This can be set in the configuration. Set a reasonable time, depending on your organization. You can also enable the archive mailbox. This can be done in the gui or with PowerShell. 


Microsoft Office and Office365 can run slow a lot of times. The software packages are large and take a lot of resources. There is nothing we can do about it. However, when you notice your machine doing things slower, it is useful to go through these steps. I have seen it many times and these steps I have talked about are what have helped.