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How to Resolve Outlook OST File Size Increasing Error

Mariya Beckham ~ Published: 08-Aug-2017 ~ Tech Query, Technology ~ 4 Minutes Reading

Emailing is not just a preference today but a requisite for any operational setting, be it personal or professional. The exchange has come up as a great solution for many big and small enterprises. OST files in Exchange are the offline folder files, which can be used even when Exchange is in offline mode. Owing to great use, When the Outlook OST file size increasing constantly more and more emails keep on downloading and a large amount of data keeps on adding, which makes Outlook OST file size too big. The maximum file size increasing the limit for OST files in Unicode format is up to 20GB for Outlook’s version 2007 and this limit is up to 50GB for Outlook’s versions 2010, 2013 and 2016.The default size is set to 20GB max. When any OST file goes beyond this limit or sometimes when an OST file tends to reach this size limit, any of the errors mentioned underneath can be encountered:

Note: OST files even consist of Shared Folders data, data contained in mailboxes as well as Public-Folders’ data, if the profile has been configured to Download-Shared-Folders. This can be easily checked as follows:

  • Under File/Tools in Outlook

  • Then Account Settings

  • After that double-clicking on Exchange address

  • Then, More Settings

  • Finally in Advanced

Modifying UNICODE’s Registry-Values for Increasing Size Limit

Registry-entry, MaxLargeFileSize. This helps in determining the absolute max size, which both PST files, as well as OST files, could possibly grow up to the level of. If size limit of Outlook OST file size too big then MS Outlook won’t allow the files to increase size beyond this size.Registry-entry, WarnLargeFileSize. This helps in determining the max amount of data, which both, the Outlook’s PST files, as well as the offline OST files, could possibly possess. If and when this max data limit has been reached, both types of files, i.e. files with (.dot)format and (.OST) extension are not allowed to add any more data to them. But, still, the size of physical files might augment due to some internal processes.

Useful Note: The above settings would apply to OST files as well as to PST files of Outlook. If any user modifies any of these registry settings or values, then it might affect the OST files, which come in use with Exchange’s Cache Mode, and sometimes with AutoArchive, and also with PST files.

Manual Methods to Fix Outlook OST File Size Increasing

  • Open Registry

  • Go to Start

  • Then type regedit in Search field

  • Then, navigate to

  • For Microsoft Outlook 2007: HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Outlook\PST

  • For MS Outlook 2010: HKEY_CURRENT_USER\Software\Microsoft\Office\14.0\Outlook\PST

  • For Outlook 2013 version: HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Outlook\PST

  • For MS Outlook 2016 edition: HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\PST

  • In right pane, right-click MaxLargeFileSize

  • Then Modify

  • After that type in the Value-Data box

  • Value must be typed in MB

  • Click Ok

  • In right pane, right-click WarnLargeFileSize

  • Then Modify

  • After that type in the Value-Data box

  • Value must be typed in MB

  • Click Ok

Important Note: It is never recommended that any user has any file size increasing larger than size 20GB. So, as an alternative, users can decrease the size of their mailboxes with the help of Outlook’s Archiving feature.

Great Alternative to Fix Outlook OST File Size Increasing Error

Sometimes OST files keep on growing & are about to reach the threshold limit. Also, when the manual techniques also fail to deliver any results then users can always turn towards some good third-party solutions. This is because professional intervention does cost a little but at the end of the day, the results are guaranteed and no data loss threats or any other risks are associated as with such an alternative, users are already dealing with expert professionals and expert solutions. One such tool is SysTools OST Splitter, which can be used to divide multiple OST file by size with ease by any users with any amount of technical understanding, as this tool is easy-to-use even for novice users.

Concluding Notes

The above article talked about the problem for Outlook OST file size increasing in which we observe that OST file size growing constantly in the maximum allowed size limit and how to resolve such issue cases. Some techniques are given to reduce file size increasing issue in Outlook OST file, which can be tried. If not, then the mention of third-party tool would surely help in this regard. Sometimes, when manual techniques do not help much, then in those cases, third-party tools always come as a ray of hope for users, by and large.

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