Outlook Client – How to speed it up

There are some amazingly easy habits you can use to make sure your Outlook Application performs properly. Whether you are using Outlook in an Office 365 environment or in a on-site or hosted Exchange environment, the suggestions here will make sure you don’t spend time watching the spinny circle thing or the faded grey screens as Outlook attempts to negotiate with it’s mail host.

Critical Path Folders – keep them lean

There are five folders in Outlook that should be kept as lean as possible or they can begin to affect the response of the Outlook client. These are “Inbox”, “Sent Items”, “Deleted Items”, “Calendar”, and “Contacts”. Microsoft documents the recommended limits of these folders for the most current versions of Outlook, but the limits are different for the different versions of Outlook. My recommended limits are:

  • Inbox: 5,000 items
  • Sent items: 5,000 items
  • Deleted items: 5,000 items
  • Calendar: 5,000 items
  • Contacts: 5,000 items

This is perhaps the main reason Outlook begins having issues. There are a number of things you can do to manage the folder sizes.

Create folders to file things away

This is a straight-forward concept. Just like you may create a folder structure in your Windows Explorer or Mac Finder to save files in some logical way, do the same thing in Outlook. Don’t just let the mail items build up forever and ever, because they will. Before long your Inbox and Sent Items will be growing beyond the limits and Outlook will suffer.

The key here is creating the folder OUTSIDE of your Inbox. The most common mistake it to create the folder inside your inbox. This does not help at all to limit the number of items in the Inbox. The items in your sub-folders count against the total for the Inbox. The following is BAD.

When creating the folders, don’t highlight the Inbox, instead select the very top heading in your outlook (usually the one showing your email address) and create the folder there. Typically I will create ONE folder like this, call it something generic like “File Cabinet”. Then start creating all my other folders below this folder. Below, notice that the File Cabinet folder is not located inside the Inbox folder.

Remember that Sent Items exists

The next most common mistake is that people do not manage their Sent Items at all. Effectively people are not really aware that the Sent Items folder exists. Treat your Sent Items like you would treat your Inbox.

What I do to remind me to manage the Sent Items is to make it part of my normal view. This is easily done by creating a “Search Folder” in Outlook that has the following properties, the folder simply shows ALL items in the Inbox and in the Sent Items folders as one view:

Then I place a reference to that Search folder in my “Favorties” in the Outlook window:

Then I setup the Outlook Options to open this folder when I start Outlook:

Now when I open Outlook, it opens to this folder, and I can see items people send me, and items I send to people, and manage them simultaneously. This also allows the flow of email to and from you and your contacts to make more sense. I omitted the names and subjects in this graph but you can see chronologically how the Inbox and Sent Items are related.

Now do something with these items

Now that you have folders to files things, use them. Get in the habit of doing something with the items in your Inbox and Sent Items.

  • Read … then decide …
  • Mark it for follow up if appropriate …
  • File it away in your File Cabinet folders …
  • Or delete it!

I’m already too messy.

It is never too late to start.

You can easily drag and drop items and entire folders into other folders. Even if you want to just solve a performance issue and believe it might because you have 100,000 items in your Inbox and/or your Sent items, then create a folder outside of the Inbox called Older Inbox Items, and shift click the majority of the items you have likely not looked at for years, and drag them all out of the Inbox into the Older Inbox Items. Outlook will take time to make this happen, so go get lunch while it processes this operation.

This applies to the Sent Items too.

You can revisit these folders if needed and even file things away at a later date. But at least you’ve given Outlook the breathing room it needs to solve a performance issue

Delete Your Trash once in while

This is often overlooked as well. On Office 365 and most Exchange environments, especially those managed by NMJ Technology, you do not need to worry about losing anything you might have thrown in your Deleted items folder and then Emptied it. We can recover things.

But rule of thumb, DO NOT TREAT YOUR DELETED ITEMS FOLDER LIKE A FILE CABINET. You will be surprised how many people throw things away in the deleted items folder thinking they can refer to it later. When you throw away a piece of paper in your physical trash can, do you routinely go back into the dirty trash can and look for it? No. And if you do, STOP THAT.

Even if you do not empty your own trash, you never know when an administrator might force this to happen. Expect that your deleted items trash can WILL get emptied once in a while. So if you want to pack rat the item, put it in the File Cabinet folders you create as I stated earlier.

Make sure when you throw something away that you don’t need it. Then Empty your Deleted Items. My outlook is set to empty the Deleted items when I close Outlook. That’s good practice.

50 Gigabyte Limit

Be aware that Outlook has a 50 GB limit for the total size of your mailbox. When Outlook hits this limit, it WILL perform very VERY badly. There are things your administrators can do to fix this, but requires hacking your computer registry to do it. We’d love you to avoid reaching this point. 50 GB is a HUGE mailbox. I have been pack-ratting mail in the same mailbox since email was invented, and even now my mailbox is only 33 GB in size. I am sure 20 GB of that mail I don’t need. But we do this.

It is relatively good practice to follow the recommendations in this post to keep your Outlook mailbox size lower, and you will have less chance to hit this 50 GB limit.

You can view the size of your mailbox in the “Mailbox Cleanup” tool in Outlook. You want to look at the “Server Data” size to know the total size of your mailbox. It it is larger than 50 GB (50000000 KB), you might be having this issue. Contact your administrator and refer them to this post for an explanation.


There are other factors that can affect the performance of your Outlook client, but these are the common issues most of my end users experience, and the steps I take to help to solve them.

If you have any doubts, reach out to NMJ Technology LLC for assistance.

Phone: 330-283-6902
Email: support@nmjtechnology.com

I have been in the Information Technology Consulting business since 1987. I studied at Kent State University in the field of Industrial Technology with the desire to become an electrical engineer like my father before me. My segue into computer networking was a complete surprise that I gladly accepted as a way to move forward in my experiences. I learned networking from the Novell point of view, and that eventually led me into the Microsoft world which is where I have become an exceptional consultant. Away from business, I continue to perfect my musicianship and write music. I have a lovely wife, and darling daughter, and super step son, two cats, a dog, and some gold fish in my pond.