Is Outlook running slow, freezing or taking too much time to load and open emails / folders? It happens due to Outlook mailbox full, damaged PST or OST files, connected third-party add-ins, or synchronization settings.
But we can make Outlook faster by optimizing mailbox, removing unwanted data, disabling add-ins etc., and repairing damaged files. Sometimes, simple mailbox maintenance can speed up Outlook performance, making it faster and more responsive without reinstalling the application.
As we know MS Outlook used to handle emails, calendars, contacts, and tasks efficiently, but continuous usage can affect your Outlook performance as it grows over time. But do not worry, this guide explains why it happens, how to speed up Outlook performance using practical methods etc.
Why Does Outlook Running Extremely Slow?
MS Outlook processes much more than just emails. Every time you start Outlook, it starts loading profile data, PST and OST file data, synchronizes with the mail server, indexes emails for search, load other data such as contacts, calendars, and notes. As mailbox data grows, additional features are enabled in background, and these operations require more time and system resources.
As a result, users may experience:
- Slow Outlook startup.
- Delayed in folder switching.
- Search results may take long time.
- Outlook is freezing and not responding.
- Unable to send and receive emails.
- High CPU or memory usage.
These are the main causes of Outlook running slow issue:
- Using older Outlook version may affect performance.
- Other custom views or clutter folders might slow down or delay the responsiveness of MS Outlook.
- Third-party or incorrectly installed add-ins may affect performance.
- Yes, large mailbox size is another reason Outlook running slow.
- Maybe your files are damaged and corrupt.
- Due to damaged Outlook profile.
- Long synchronization periods in Cached Exchange Mode.
How Does Mailbox Size Affect Outlook Performance?
Large mailbox size is one of the biggest reasons for Outlook running extremely slowly. Generally, Outlook stores data in PST and OST files.
When these data files grow, it starts affecting Outlook performance. The latest versions of Outlook support data files up to 50 GB. If your files grow more than this size, it may become corrupt and unable to access data.
So, before these situations, we will resolve this issue and speed up Outlook performance by following the mentioned techniques. Before choosing any technique, check the mailbox size first.
How to Check Outlook Mailbox Size?
- Open your Outlook.
- Go to “File” >> “Tools” options.
- Choose “Mailbox Cleanup”.
- Hit on the “View Mailbox Size”.
Now here you can optimize which folder or item is taking up more storage space. Generally, 15-20 GB for PST and 20-30GB for OST file sizes are recommended. If it crosses, then Outlook starts running slowly and showing errors.
How to Speed Up Outlook Performance?
We have multiple techniques to make Outlook faster. First, we will start with basic and necessary techniques, and then smart ways. All methods are given below one by one:
# 1: Turn Off Unwanted Add-ins
Sometimes third-party add-ins may affect and make Outlook extremely slow. So, we will start Outlook in safe mode, because it will disable all add-ins, and if it works then it means third-party add-ins are affecting performance and help to speed up Outlook.
- Open “Run” using “Windows + R” keys.
- Type: exe /safe and “Enter” button.
- Choose “OK” button.
If your Outlook works properly and smoothly without running slowly. Then follow these steps to remove add-ins.
- Head to the “File” tab.
- Choose “Options” >> “Add-Ins” >> “Manage COM Add-ins” >> “Go” options.
- Remove all unwanted add-ins from here.
- And try to start Outlook again to speed up Outlook.
# 2: Update Windows and Outlook
If you are using older version of Outlook and system, then update it following these steps:
- For Outlook: Office Account > Update Options > Update Now.
- For Windows: Update & Security > Windows Update > Check for any updates.
# 3: Speed Up Outlook by Rebuilding Search Index
If your emails are missing from search results, delayed in searches, and incomplete search results, it means Windows Search Indexing is affecting performance and makes Outlook running slow.
- Open “Control Panel”.
- Choose “Indexing Options”.
- Click on “Advanced” button.
- Choose “Rebuilt” under “Index Settings”.
- Select “OK” when a prompt appears.
# 4: Limit Cached Exchange Mode Synchronization
This is mainly for Microsoft 365, Exchange Server, or Outlook.com account users; Outlook stores a local copy of your mailbox in OST format. It is also known as Cached Exchange Mode and allows you to access emails even when you are not connected to the internet.
A large downloaded mailbox can affect your Outlook performance and also increase OST file size. So, we will change settings to speed up Outlook performance and prevent your OST file from being corrupted.
- Open your MS Outlook.
- Head to the “File” >> “Account Settings” >> “Account Settings”.
- Choose your “Exchange or Microsoft 365” account.
- Hit the “Change” button.
- Find the “Mail to Keep Offline” slider.
- Choose short sync period.
- Select the “Next” and “Finish” buttons.
- Restart your Outlook.
Which Sync Duration Should You Choose?
| Mailbox Size | Recommended Offline Period |
| Up to 10 GB | 1 Year |
| 10–25 GB | 6 Months |
| 25 GB+ | 3–6 Months |
# 5: Split and Manage Smaller Parts than Large Data Files
As PST file grows, Outlook starts the process with large dataset every time it starts, and it affects Outlook performance with large mailboxes. Manual techniques help with smaller file sizes or removing unwanted data which is a time-consuming process.
But in case you don’t want to delete any item or have large PST file, then splitting is the only way to manage your mailbox properly. Install the SysTools PST Splitter to handle large PST files by size, folder, date, year, category, subject etc., accordingly.
This software can handle from 1 MB to 1 TB smoothly, and it doesn’t modify or delete any items from your mailbox data. Download the demo edition for trial.
# 6: Archive Old Emails Frequently
Archiving old emails is another safe method to speed up Outlook performance. In case your mailbox has old emails then simply archive and keep them in separate PST file for future access.
- Open Outlook.
- Navigate the “File” tab.
- Choose “Tools” >> “Clean Up Old Items” >> “Archive” option.
- Select “Archive this Folder” and “All Subfolders”.
- Select required folders to archive such as: Inbox, Sent Items, etc.
- Give a name to your file and choose “OK” to start archiving issue.
If you are archiving data automatically through archive policy then your separate PST will connect with your Outlook profile. And if you are doing it manually, Outlook will create a separate disconnected file, which you can access by importing.
# 7: Speed Up Outlook by Removing Empty Space by Compacting PST
Deleting emails or items from PST file doesn’t automatically reduce PST file size. Sometimes, space remains inside the file.
- Launch your Outlook.
- Head to the “File” tab.
- Choose “Account Settings” >> “Account Settings” >> “Data Files” >> “Settings” >> “Compact Now” option.
# 8: Remove Duplicate Emails
Duplicate emails are the common reason for increasing Outlook data files and making Outlook running slow. Manually discarding them is a tough and time-consuming process, so you can take help of SysTools Outlook Duplicate Remover Tool, which automatically detects and deletes duplicate items from the mailbox in a few seconds.
Manual technique contains risk of accidental deletion, so it is better to use a professional solution. It can:
- Ensures to speed up Outlook performance, so that no user will face any duplication in their mailbox.
- This proactive tool eliminates many duplicate items like emails, tasks, notes, contacts, and calendar events without losing important data.
- It offers dual options to upload files across or within folders, with quick batch removal.
# 9: Speed Up Outlook by Fixing Corrupt Outlook Profile
The Outlook profile contains all settings and data, if profile becomes damaged, Outlook may experience performance issues. Outlook running slow and profile corruption may occur due to improper Outlook shutdowns, Office updates, damaged configuration files, synchronization failures, or system crashes.
We will make Outlook faster by repairing a damaged profile, and if it doesn’t work then creating a new profile.
- Open your MS Outlook.
- Choose “Account Settings” >> “Account Settings” from “File” tab.
- Choose affected account under the “Email” tab.
- Select “Repair” option.
- Now try to restart Outlook.
This process checks account settings, connectivity and profile configuration issues that may affect performance. You can also create a new Outlook profile to speed up Outlook.
# 10: Create a New Outlook Profile to Fix Outlook Running Slow
- Firstly, close your Outlook completely.
- Open your “Control Panel”.
- Choose “Mail (Microsoft Outlook)”.
- Select the “Show Profiles” option.
- Hit on the “Add to create a new profile”.
- Enter a profile name and choose “OK” button.
- Provide email account information and after completing it, return to the “Mail” window.
- Choose “Prompt for a profile to be used” or choose your newly created profile as the default under “When starting Microsoft Outlook, use this profile”.
- Hit the “Apply” and “OK” buttons.
- Now try to restart Outlook with new profile.
# 11: Repair Damaged Outlook Data Files
In most cases, Outlook data files PST and OST get corrupted due to exceeding the suggested size. And recovering data from damaged file is not an easy task. Microsoft provides ScanPST.exe to repair damaged PST and OST files (mainly for PST). If your Outlook data files are minimally damaged then follow mentioned steps to speed up Outlook:
- Firstly, locate your ScanPST.exe in the common locations:
Outlook 2016, 2019, 2021, and Microsoft 365 (64-bit) – C:\Program Files\Microsoft Office\root\Office16\
Outlook 2016, 2019, 2021, and Microsoft 365 (32-bit) – C:\Program Files (x86)\Microsoft Office\root\Office16\ - You can search for SCANPST.EXE if you cannot find it in these folders.
- After locating, open “SCANPST.EXE”.
- Use “Browse” button to load data files.
- Select your PST file and use “Open” button.
- Select the “Start” button to analyze PST file.
- Lastly, hit the “Repair” button to complete process.
What If Your Data Files are Severely Damaged?
Manually it is not possible to recover data from severely damaged data files. In such cases, only professionals’ tool can help to repair and restore data properly to speed up Outlook.
You can take help of SysTools PST Recovery Tool to fix the corruption and restore data into healthy format. It uses advance scan mechanism to repair corrupt PST file whether it’s severely damaged. It works with ANSI and UNICODE PST files exported from any Outlook version.
And SysTools OST Recovery tool for damaged OST files. It can also restore complete data including permanently deleted data into healthy formats such as PDF, PST, EML, MSG, and HTML. It works with orphaned, damaged, and inaccessible OST files without affecting or losing original items. You download free demo version of both solutions according to your needs.
Additional Tips to Speed Up Outlook Performance
Apart from suggested techniques, you can follow these small steps to make Outlook faster and improve.
- Always delete unnecessary synchronization logs from sync Issues, conflicts, and local failures.
- Multiple rules can also increase the processing time.
- Try to update older versions of Windows and Outlook on time.
- Multiple antivirus programs continuously scan Outlook data files and this can affect performance.
- Clean your Trash and Spam folders regularly.
- Remove large attachments from the mailbox or you can save them locally.
- Always start Outlook in Safe Mode to identify problematic add-ins.
Conclusion
Multiple factors affect Outlook performance such as large mailbox size, folder organization, synchronization settings, add-ins, search indexing, damaged data files etc. And here we have discussed the techniques to speed up Outlook performance by archiving old emails, removing unwanted items, upgrading Windows and Outlook versions, or managing your data files into smaller parts.
This blog has covered all important topics like why it happens, how it impacts, possible manual techniques, and smart alternative solutions for large mailboxes and damaged data files. If you face any issue during process, you can connect with us through 24*7 live chat support.
