Seeking Assistance: Outlook Warning, Storage, and OST File Limit

[Frank_Lee]

Hello Microsoft community,

I am reaching out for assistance regarding a couple of concerns I've encountered while using Outlook. I hope someone can provide valuable insights or direct me to the right resources.

Outlook Warning Window:
Recently, I encountered a warning window when attempting to delete an email from my Outlook inbox. It's worth mentioning that I was actively editing and sending emails at the time, and no issues arose during those processes.

Mailbox Storage Limit:
Despite having a total mailbox storage of 100GB (50GB default + 50GB from an additional plan), I've noticed that my Outlook storage is at its maximum capacity, currently at 56 GB. Interestingly, I haven't faced any problems receiving or sending emails today.

OST File Limit:
I've been informed by IT that, despite the expanded mailbox storage, the maximum limit for a single .ost file remains at 50GB. Can someone provide guidance on managing this situation or suggest best practices?

I appreciate any assistance you can offer. Thank you in advance for your help!

Best regards,

Frank Lee

[#2]

Hi @Frank_Lee,

here are some insights regarding the issues you raised:

- Outlook Warning Window: The warning you received is a result of your Outlook data file (`.ost`) reaching its maximum size. To resolve this, consider permanently deleting unnecessary items to reduce the file size.

- Mailbox Storage Limit: Outlook accounts allow up to 100GB of storage per mailbox. If your mailbox is nearing its limit, Outlook will notify you via emails and in-app messages. You can use Mailbox Cleanup, a one-stop-clean-up tool you can use to trim the size of your mailbox.
Manage my mailbox size - Microsoft Support
Mailbox storage limits in Outlook - Microsoft Support

- OST File Limit: The maximum OST file size depends on your Outlook version. Versions 2010 and later support up to 50GB, while earlier versions support up to 20GB.
You can adjust the maximum size through registry entries. 
How to configure the size limit for both (.pst) and (.ost) files in Outlook - Microsoft Support

Please click Mark as Best Response & Like if my post helped you to solve your issue.
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Kindest regards,

Leon Pavesic
(LinkedIn)

[#3]

@LeonPavesic

Hi LeonPavesic,

Thank you for your insights on the issues I raised. I have a follow-up question regarding the warning message I received about my Outlook data file (*.ost) reaching its maximum size. I currently have a total mailbox storage of 100GB (50GB default + 50GB from an additional plan), and I've only used up 56GB. Despite this, I'm still encountering the warning message.

Could you clarify if the warning is specifically related to the .ost file exceeding 50GB, even if the overall mailbox storage is 100GB? And is there any way to extend the .ost file limit beyond 50GB?

I appreciate your assistance.

Best regards,
Frank_Lee

@LeonPavesic 

[#4 · Accepted solution]

Hi @Frank_Lee,

thanks for the update.

This issue is specifically related to Outlook 2010 and later versions, where the default maximum size for .ost files is set at 50GB, independent of your overall mailbox storage.

Despite having a 100GB mailbox, the .ost file has its own size limit, leading to the warning message you're seeing.

To manage this situation, consider the following options:

1. Clear Out the Mailbox: Regularly delete unnecessary emails and attachments, and empty the "Deleted Items" folder.
2. Adjust "Mail to Keep Offline" Settings: Reduce the amount of mail kept offline in the OST file.
   Work offline in Outlook - Microsoft Support
3. Move Mail Items to Archive Folder: Move older items to an Archive folder.
   Archive in Outlook for Windows - Microsoft Support

If needed, you can increase the .ost file limit beyond 50GB by adjusting registry entries.
https://support.microsoft.com/en-us/topic/how-to-configure-the-size-limit-for-both-pst-and-ost-files...

Please click Mark as Best Response & Like if my post helped you to solve your issue.
This will help others to find the correct solution easily. It also closes the item.

If the post was useful in other ways, please consider giving it Like.

Kindest regards,

Leon Pavesic
(LinkedIn)