Fix Outlook.ost Has Reached Maximum Size in Outlook 2019, 2016, 2013, 2010, 2007

Written By Andrew Jackson
Anuraag Singh
Approved By Anuraag Singh
Published On September 13th, 2022
Reading Time 5 Minutes Reading

Microsoft Outlook application uses PST and OST files to store the mailbox data. OST or offline storage table is exactly the user mailboxes on the exchange server. When the internet connection gets established, all the modifications done in the offline mode get synchronized with the Exchange server.

How do you feel when the user opens an Outlook application and a message displayed on the screen Outlook.ost has reached its maximum size? It is a very annoying situation for all MS Outlook users. Deleting contents from the OST file is only the option left out. So In this article, we are going to discuss the reasons behind this problem. And also we will discuss the step-by-step process to tackle this issue. So keep reading here…

Problematic Error Emergence:

Outlook.ost Has Reached Its Maximum Size


Default Outlook Profile.ost has reached the maximum size

Symptoms: Outlook.ost has Reached Maximum Size

When a user opens or uses the MS Outlook program, sometimes an error message emerges that says:

Similar Post: Fix Outlook Data File Has Reached The Maximum Size Error

Possible Reasons Behind The Error

There are several reasons for the occurrence of such an error: outlook.ost has reached maximum size 2016, 2013, 2010 & 2007, which are as follows:

  • The user’s ANSI-encoded PST file or OST file is bigger than the size limit or may be approaching that 2 GB size limitation.
  • Unicode-encoded PST file or OST file is bigger than the size limit or may be approaching that 50 GB size limitation.
  • There is some registry setting/policy in place, which might have changed the limits that are there by default causing this error: Default Outlook Profile.ost has reached the maximum size

Outlook.ost Has Reached Maximum Size Solutions at Hand

The choice of the most befitting solution for this particular problem depends on the type of scenario (from the above) that is affecting the Outlook data file which is in question. Following ways can help in finding solutions to this error: Outlook.ost has reached maximum size 2019, 2016, 2013, 2010, 2007.

Determine Outlook Data File’s Type

  • Outlook program must be closed first
  • Go to Start
  • Then, Control Panel
  • Then, Mail
  • Now, click “Data Files…”
  • Double-click that particular Outlook data file, which is in question
  • If the “MS Exchange” window shows up, then the file is .ost
  1. Click the “Advanced” tab
  2. At the bottom, see the message that declares “Mailbox Mode” either as Unicode or as non-Unicode
  3. Note the mode indicated
  • If the “Personal Folders” window comes up, then that file is a PST file
  1. Search the box names “Format:”
  2. If the value is “Personal-Folders-File (97-2002)”, then it is an ANSI format file
  3. If the value is “Personal-Folders-File” then it’s clearly Unicode
  4. Note the type

Locate Outlook Data File

  • Ensure Hidden Files aren’t hidden
  1. For this, go to Tools in any of the Explorer windows
  2. Then Folder Options…”
  3. And then click the “View” tab
  4. Now select the radio button
  5. The radio button is for “Show hidden files…”
  6. In Win 7, if there isn’t any menu bar with the option “Tools”, hit the ALT key for making it appear
  7. In MS Windows 2K/XP version, the default location is C:\Documents and Settings\-your-username-here\Local Settings\Application Data\Microsoft\Outlook\
  8. And in Windows Vista/7 edition, this default location is C:\Users\-your-username-here\AppData\Local\Microsoft\Outlook\
  • If MS Outlook is in use with an MS Exchange server, then there would be 1 or more than 1 OST in this particular folder, else, there would be 1 or more than 1 PST files

Convert ANSI-Encoded PST to UNICODE Format

  • Try creating a new Outlook profile with some new, empty PST file
  • If the Outlook version is newer than version 2003, then this new PST would be of Unicode format by default
  • Import old PST file into new PST

Convert ANSI-Encoded OST File to Unicode Format

  • First, “Cached-Exchange-Mode” has to be disabled
  • Rename the OST file that is in question to the name “outlook.old”
  • And now, open Outlook
  • Close Outlook now
  • Now, try re-enabling the “Cached-Exchange-Mode”
  • MS Outlook program would rebuild the OST file in Unicode format along with data from the MS Exchange server
  • As per the mailbox size, this can take some time

The Umbrella of Comfort with Third-Party Software

Where manual methods tend to fail often while solving errors like outlook.ost has reached maximum size, expert third-party tools come as the ray of hope as they are adept in their job. Being developed by master-thinkers, these tools have come a long way after rigorous rounds of R & D and after quality testing; so they mostly do not go wrong.

One such brilliant solution that would serve the purpose well in such a scenario is the SysTools OST Splitter Tool. You can get to see its demo model as well before finally jumping to the conclusion to buy it; so the whole transaction would be a very transparent one, with no hidden agendas of the vendor. As a matter of fact, this is a very popular tool in this sphere.

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With the growing number of email items every day, the Outlook data files tend to grow in size considerably. There is a default limit set for each type of file, exceeding which can result in damage and the errors like outlook.ost has reached maximum size. But solutions are also there to combat this situation. There are ways by which one can get away with such problems. All the possible solutions have been talked about in this blog to tackle Outlook.ost has reached its maximum size issue.