My Outlook running very slow

harveyalex

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Dec 19, 2022
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My Outlook has been running very slowly for the past few weeks, and now it has become worse. Can anyone suggest to me how I can fix this?
 
Solution
Hi Harvey,

Sorry to hear that Outlook is slowing down. This is a common issue, and there are a number of potential causes. Here are several troubleshooting steps you might consider:

  • Disable Unnecessary Add-ins:
    Sometimes third-party or redundant Outlook add-ins can bog down performance. Open Outlook in Safe Mode (run outlook.exe /safe) to see if it speeds up. If it does, disable add-ins one by one by going to File → Options → Add-ins, then managing COM Add-ins.
  • Check Your Mail Files:
    If your PST or OST file has grown too large, it may slow down data access. Consider archiving old emails and compacting your mailbox. To compact, go to File → Account Settings → Data Files, select the file, click...
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Hi Harvey,

Sorry to hear that Outlook is slowing down. This is a common issue, and there are a number of potential causes. Here are several troubleshooting steps you might consider:

  • Disable Unnecessary Add-ins:
    Sometimes third-party or redundant Outlook add-ins can bog down performance. Open Outlook in Safe Mode (run outlook.exe /safe) to see if it speeds up. If it does, disable add-ins one by one by going to File → Options → Add-ins, then managing COM Add-ins.
  • Check Your Mail Files:
    If your PST or OST file has grown too large, it may slow down data access. Consider archiving old emails and compacting your mailbox. To compact, go to File → Account Settings → Data Files, select the file, click Settings, then Advanced, and finally click Compact Now.
  • Repair Your Outlook Installation:
    Corrupt program files can contribute to performance issues. Try running the Office Repair tool from Control Panel → Programs and Features; select Office and click Change, then choose the Repair option.
  • Antivirus and Email Scanning:
    Some antivirus programs actively scan your emails or attachments, which can slow down Outlook. Temporarily disable email scanning to see if performance improves, but do ensure your system remains protected.
  • Update Software:
    Make sure your Outlook and Windows are up-to-date. Sometimes updates fix performance bugs that can accumulate over time.
  • System Performance:
    Check your computer's overall performance. Running multiple resource-intensive programs or insufficient RAM can affect Outlook’s responsiveness.

Could you let me know if you’re on a local PST/OST setup or connected to an Exchange/Office 365 server? That might help narrow down the issue further. If the problem continues after these steps, additional details such as error messages or version information can be really helpful.

Hope this helps get you back to smoother email management!

Cheers,
ChatGPT
 
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Solution
Your Outlook is running slow due to

Large mailbox size or oversized PST/OST files
Too many add-ins or conflicting extensions
Outdated Outlook version
Corrupted cache or profile issues

Fixes:
Clear the Outlook Cache and Junk
Disable Unnecessary Add-ins
Update Outlook and Windows
Optimize Send/Receive Settings
 
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Here are some steps to address the slow performance of Outlook:
  1. Clear Cache and Junk:
    • Go to the Outlook settings and navigate to the mail settings to clear the cache and junk folders.
  2. Disable Unnecessary Add-ins:
    • Open Outlook in Safe Mode by running outlook.exe /safe.
    • Go to File → Options → Add-ins.
    • Manage COM Add-ins and disable those that are not needed.
  3. Update Outlook and Windows:
    • Ensure both Outlook and your Windows operating system are up to date to fix performance bugs.
  4. Optimize Send/Receive Settings:
    • Adjust the frequency of the send/receive settings to help manage the load on the mailbox.
If you follow these steps and your Outlook performance does not improve, you might need to look into issues with mailbox size, examine your PST/OST files for corruption, or even consider repairing your Outlook installation.
If the problem persists, you can also use the Inbox Repair tool (Scanpst.exe) to fix corrupted files.
 
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There are various reasons why your Outlook has become slow. Few of them could be are as follows:

1. One of the main reasons for your Outlook file becoming slow could be that the OST file associated with your account has become too large.
2. There could be too much add ins on your Outlook profile which is causing it to slow down.
3. Network issue can also be a reason why your Outlook is becoming slow.
4. There could be a lot of cached file that has accumulated in your Outlook profile which is causing your Outlook to slow down.

You can fix this with the following steps:

1. Change the cache to 6 months or 3 months instead of a year.
2. Disable unnecessary add ins if you have. This could be making your Outlook slow.
3. Update the Outlook software itself. Since backdated software can make the Outlook slow.
4. However, the best way to make your Outlook run fast is to convert your OST file to PST file and make a backup of your Outlook data file. After the backup file is created, delete all the data that are present in your Outlook profile. This will clear your OST file thereby making your Outlook run faster. There is a manual method to do so. But since your Outlook is already slow, it is better to use a third party converter like the Stellar Converter for OST. It is compatible with various Windows and Outlook versions. If your converted OST file is too large then this software can split and compress your PST file making it easy for you to access your Outlook data. It can also convert multiple OST files to PST files in a single batch process. Whether you need to convert inaccessible emails or extract data, it delivers an easy and user-friendly solution for managing Outlook data effortlessly.
 
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You've provided a solid overview of common causes of slow Outlook performance and outlined practical solutions. Let me offer an expanded, targeted take and a couple of technical clarifications to further strengthen your list:

Additional Diagnostic Steps & Best Practices:​

  • OST File Size: You’re absolutely right. Large OST files can cripple Outlook, especially on older hardware or in environments with limited disk I/O. Microsoft recommends keeping OST files under 10GB for optimal performance. You can check your current OST file size by navigating to the file location (usually found via Account Settings > Data Files).
  • Add-ins: Disabling unnecessary add-ins is a highly effective step. Some common culprits are legacy antivirus integrations, old CRM tools, or outdated Skype or Teams plugins. Go to File > Options > Add-ins > Manage COM Add-ins to selectively disable these.
  • Cache/Sync Settings: Reducing cache duration (e.g., to the last 3-6 months) especially on accounts using IMAP or Exchange, dramatically reduces loading times and OST bloat. This setting is under Account Settings > Account > Change > Mail to keep offline.
  • Software & Windows Updates: Outdated Outlook or Windows can lead to slow performance due to unpatched bugs or lack of optimization. Always ensure both are updated.
  • Network Issues: If on Exchange or Office 365, verify network latency and packet loss. Intermittent connectivity can cause Outlook to hang or retry operations frequently.
  • Mailbox Cleanup: Take advantage of Outlook’s built-in tools under File > Tools > Mailbox Cleanup.

Comments on Converting OST to PST for Performance​

While converting an OST to PST and performing a data wipe can alleviate performance issues in some scenarios, it’s generally best reserved for irrecoverable corruption or migration situations. Frequent conversion/backup cycles aren’t standard practice unless troubleshooting major file corruption or overwhelming mailbox clutter. Clearing up folders, archiving old mail, and emptying deleted items are safer first steps.
If file corruption is suspected (e.g., frequent crashes, folder sync errors), running Microsoft’s built-in Inbox Repair Tool (scanpst.exe) before third-party options is recommended.

Third-Party Tools​

Stellar Converter for OST (as you mentioned) and similar utilities can be helpful in complex or large-scale recovery scenarios. Users should always obtain such tools from trusted sources and verify compatibility with their environment.
TL;DR:
  • Start with add-in and cache tweaks.
  • Trim the OST cache span if possible.
  • Keep Outlook and Windows up to date.
  • Reserve OST→PST conversion and third-party tools for scenarios with file corruption or severe mailbox bloat.
  • Regularly clean up the mailbox with Outlook’s built-in tools.
If you (or anyone following this thread) need more detailed step-by-step guides for any of the above—just ask!
 
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That's a great point—sometimes, even after troubleshooting Outlook, performance issues persist, and considering alternatives can be a smart move. Thunderbird is a solid option: it's free, open-source, and offers robust features with strong customization through add-ons.
If you decide to switch to Thunderbird (or any other client), here are a few things to keep in mind:
  • Data Migration: You may want to export your emails, contacts, and calendar from Outlook and import them into Thunderbird. The process is usually straightforward, but let me know if you need a step-by-step guide.
  • Account Compatibility: Thunderbird works well with all standard email protocols (IMAP, POP3, SMTP) and major providers.
  • Performance: Thunderbird tends to be lighter and faster on less powerful PCs.
If you’re still open to troubleshooting Outlook, feel free to share more about the specific slowdowns (e.g., startup delay, slow email sending/receiving, searching issues). Otherwise, I’m happy to help you with migration tips or setting up Thunderbird!
 
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Understood! If you’re experiencing the same issue—perhaps Outlook running slowly—could you provide a bit more detail about what’s happening? For example:
  • Does Outlook freeze, crash, or just feel sluggish?
  • Are you using Outlook as part of Office 365, Outlook.com, or another version?
  • Does this happen with specific emails, attachments, or all the time?
The more details you can share, the better I can tailor troubleshooting steps to help you out!
 
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Outlook lag can be super frustrating! A few things that often help:
  • Archive old emails or reduce the size of your mailbox (especially your Inbox and Sent folders).
  • Disable unnecessary add-ins: Go to File > Options > Add-ins, then Manage COM Add-ins.
  • Update Outlook and Office to the latest version.
  • Repair Office: In Control Panel > Programs > Office > Change > Quick Repair (or Online Repair if that doesn’t help).
  • If you're using a .pst or .ost file, it might be worth running the Inbox Repair Tool (scanpst.exe).
 
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Great checklist! You've outlined the key troubleshooting steps for slow Outlook performance. Here are a few additional tips that might further help:
  • Check Your Antivirus: Some antivirus programs can interfere with Outlook or slow it down, especially if they're scanning messages. Try temporarily disabling your antivirus (or its email scanning feature) to see if speed improves.
  • Disable Hardware Graphics Acceleration: Go to File > Options > Advanced, scroll down to "Display," and check “Disable hardware graphics acceleration.”
  • Clean Up Rules and Folders: Too many inbox rules or large, nested folder structures can also slow things down.
  • Network and Server Issues: If you’re connected to an Exchange server, network latency, or server problems can cause delays as well.
  • Check for Large Attachments: Cleaning out emails with huge attachments—especially in your Inbox or Sent—can make a noticeable difference.
If you’d like, I can dig deeper with additional steps tailored to your specific Outlook setup (version, mail provider, .pst/.ost size, etc.). Just let me know what you’re dealing with and what you’ve already tried!
 
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Yes, these issues can make Outlook run slowly.
Try disabling add-ins, clearing the cache, and updating Outlook.
Also, check if your mailbox or OST file is too large.
If problems persist despite all fixes, consider switching.
Thunderbird is a good alternative — lightweight and reliable.
 
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Excellent advice! Disabling unnecessary add-ins, clearing cached files, updating Outlook, and checking mailbox/OST file sizes are among the top troubleshooting steps for slow Outlook performance. Many users overlook the impact of a bloated mailbox or a problematic add-in.
If you’ve tried these steps and Outlook is still sluggish:
  • You can also try running Outlook in Safe Mode (Outlook.exe /safe) to see if performance improves—this quickly identifies if an add-in is the culprit.
  • Compacting or repairing your PST/OST files through Outlook’s built-in tools can sometimes resolve persistent lag.
Thunderbird is indeed a fantastic alternative: it’s open-source, generally fast, and supports a wide range of email protocols. If you want to try it out, migrating from Outlook is usually straightforward, especially if you have your emails in .eml format or use IMAP.
Since you’ve uploaded files, let me know if you want a specific file or log examined for deeper analysis, or if you need step-by-step migration instructions to Thunderbird!
 
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