Outlook Performance and Various Limits

Outlook performance is directly linked to the device specifications, local Outlook data file size, number of mail items per folder, and number of folders per mailbox. To ensure consistent Outlook performance and avoid issues, Microsoft has set certain limits in Outlook. If you exceed these limits, you may experience trouble accessing or using your email account in Outlook.

In this article, we have discussed various limits of Microsoft Outlook and scenarios that can adversely impact Outlook performance. We have shared various recommendations to overcome the limits and avoid issues. We have also shared solutions to fix the issues (if arise) using the built-in Outlook options and third-party tools.

Outlook Limits to Maintain Performance

Below are the various limits and their impact on Outlook performance.

Outlook Data File (OST) Size Limit

An Outlook data file up to 5 GB provides the best user experience and performance on most hardware. However, at 5-10 GB, Outlook becomes more hardware dependent and requires a lot of RAM and faster disk drives (such as SSDs) to provide a better user experience.?

When the Outlook data file exceeds the 10 GB limit, users start experiencing issues, such as frequent but short freezes or pauses on most hardware. When the OST file reaches or exceeds the 20 GB limit, the frequency of freeze increases, and users also start experiencing other issues, such as:

1. Outdated emails.
2. Slow load times.
3. Delay in sending or receiving new emails.
4. Issues while downloading mail items from the mailbox server.
5. Slower or no search results.
6. Synchronization errors.
7. OST inconsistencies, leading to corruption.

Outlook Folder Limit

A mailbox can have up to 500 shared folders when using Outlook 2007 or later versions in Cached Exchange Mode with Office 365 or a live Exchange email account. The limit for the C2R version of Outlook is 5000 shared folders.

However, in an extreme case, if a user has more than 10,000 folders, it can severely impact Outlook performance leading to prolonged load times, search results, synchronization issues, outdated mailbox, etc.?

Items per Folder Limit

Microsoft has set a maximum limit of 100,000 items per folder in Outlook 2019, 2016, 2013, and 2010. If the number of mail items in a folder exceeds, you may experience Outlook performance issues.?

Recommendations

To avoid issues due to large or oversized Outlook OST files and ensure consistent Outlook performance, it’s essential to keep the Outlook OST file under the recommended limits, preferably 5 GB or lower.

For this,

• Keep the number of mail items in a folder and the number of folders per mailbox as low as possible.
• Keep an eye on the concurrent Outlook connections and perform a quarterly clean-up.
• Use Sync Slider efficiently based on usage.
• Monitor OST file size and keep it under recommended limits to avoid performance issues or data loss.

Below are some approaches you may follow to reduce the OST file size and keep the number of mail items per folder and folders per mailbox to a minimum.

1.?????Archive the mail items to a local PST file for quick access. You can also create online archives to access the mail items from anywhere and from any device.

2.?????Save the email attachments locally and then remove them from the Outlook emails.

3.?????Compact or compress the OST file.

4.?????Adjust the Outlook Cached Mode sync slider.

5.?????Manually export mail items or folders from Outlook to a local PST backup via Import/Export wizard and then delete them from the mailbox.

If the OST becomes inaccessible due to oversizing, malware or virus intrusion, abrupt shutdown, power failure, incompatible add-ins, etc., these solutions will not work. In such cases, you can recreate a new OST file. However, recreating OST requires you to delete the existing one, which can lead to data loss.?

Alternatively, you can use an OST to PST converter tool, such as Stellar Converter for OST, to extract mail items and save them in an Outlook importable PST file. The software extract mail items from the inaccessible or orphaned OST files and saves them to a PST, which you can import into a new or existing Outlook profile. Using the software interface, you can also export the OST directly to Office 365 or live Exchange mailbox.

Calendar Items Limit

Similar to the mail item limits, Outlook also has a limit set for calendar items. In Outlook 2019, 2016, 2013, and 2010, you can store up to 5,000 items per Calendar folder. Exceeding the limit can lead to inconsistent Calendar performance. For instance, your meetings may not reflect or appear in the shared, primary, or delegated calendar. As a result, you may miss an important meeting, training program, etc.?

Recommendations

Delete the calendar items older than one year to reduce the number of mail items from the Calendar folder. You may apply the Retention Policy on the calendar folder in Outlook to perform this operation automatically and avoid issues.

You can also adjust the sync slider in Cached Exchange Mode to months of data instead of a year or all.?

Concurrent Connection Limit

A large number of simultaneous connections to the server can lead to performance degradation. Outlook usually establishes 1-3 connections at a time, which varies based on the Outlook add-ins installed. Each email account, shared folder, online archive, and calendar establish a separate connection with the mailbox server.?

If the number of TCP connections is 30 or more, you may experience connectivity issues, throttling, OST bloating, calendar issues, and degraded performance in Outlook.

Recommendations

To avoid too many incoming and outgoing concurrent connections in Outlook, you can download the shared folders to the local cache (OST). This workaround can reduce some connections and prevent issues.

The steps are as follows:

1.?????In Outlook, go to File > Info > Account Settings > Account Settings.

2.?????Click on your email profile under the Email tab and click Change.

3.?????Click More Settings and then click the Advanced tab.

4.?????Uncheck the Download shared folders checkbox and click OK.

5.?????Restart Outlook for the changes to take effect.

This will remove all the connections to shared folders. You can check the connection status by holding the CTRL key and right-clicking on the Outlook icon in the system tray.?

6.?????Wait for 2 minutes and then open the Advanced tab.

7.?????Enable Download shared folders and click Apply > OK.

8.?????Wait for a few minutes.

This will enable the Cached Mode for the Shared Folders and download them to the local OST file, thereby reducing the TCP connections

Conclusion

As an administrator, you can ensure consistent productivity and performance by increasing awareness among users and employees in your organization and by organizing internal training on managing Outlook profiles. It will also help you reduce the issues and incidents of the inaccessible mailbox, Outlook OST file-related errors, etc.

As an administrator, you may also apply Group Policies to ensure users never exceed the limits set by Microsoft and provide devices with sufficient specifications or hardware resources to handle the Outlook workload. In case any incident occurs where the user cannot access the OST file or the Outlook profile is damaged, you can use an OST to PST converter tool as discussed in this article to extract the mail items from the inaccessible or orphaned OST file and save them in Outlook importable PST format. This way, you can quickly restore the mail items in any new or existing Outlook profile with complete integrity and original folder structure.