What Does OLK Mean? Learn in few Steps!!!

Admin | Technology | 7 minutes read | Last updated on February 8th, 2023,

Users around the world are familiar with range of Microsoft applications and all its related productivity utilities it offers. Majority of users make use of Win OS preconfigure on machines. So, the familiarity of the brand is introduced long before and now continued till present. Outlook is constantly been one of the most successful Microsoft email app that is serving business communication.

MS Outlook is the app which has evolved desktop communication. In spite of the various options and properties it possesses, the application also comes with range of versions. Different versions supports application accessibility and its services.

Microsoft Outlook OLK File and its Data Types

Data files and its types are the storages that are preserved by the application to keep their information. The storage contains either the details of configuration or profile contents. MS Outlook is designed that carries the following file types for data storage:

PST: It is the primary Outlook supported file extension. When used individually, Outlook creates default storage in the form of Personal Storage Table i.e. PST file. The file is designed in a binary structure and contains all exchanged or generated data using corresponding profile i.e. emails, address book, calendar (events, anniversary, and meetings), journals, tasks and notes, RSS Feeds (optional). It is a proprietary data file of Outlook and can only be viewed by supported application and no other.

OST: This is a copy of the cache Exchange profile. When utilizing Exchange Server environment, then Outlook configuration with Exchange creates an Offline Storage Table i.e. OST. It is meant for offline usability when not connected with the server. And when we connect the profile with Exchange environment then synchronization takes place automatically. Again it is Outlook proprietary file format and depends on the origin Exchange profile plus environment.

OLM: It is a file that is generated by Outlook for Mac. It has similar functionality as Windows corresponding item. However, instead of OST or PST, the email client make use of OLK file format i.e. OLM to store the data of Outlook. It is not a default supported format but generated by means of export functionality included in the application. OLM is a proprietary file format of Mac Outlook and can only be readable by respective application.

Other Storage Maintenance by MS Outlook

Apart from these discussed file extensions, MS Outlook has the ability to store data in various forms. Generally, additional data types of Outlook is the transitory copy of existing contents that helps in redeveloping the storage just in case of any mishap occur by the existing means.

Database File & Temporary File

Database File: The entire profile content is maintained by the application in a database file on the backed storage. The database file includes precise data stored, exchanged, maintained or even removed by the profile. By using inbuilt Database Utility program, a user can build a profile again in case of profile corruption or deletion of data.

Temporary File: These files are maintained in the form of OLK by the profile. The .olk extension files are used to maintain the database individually of particular profile. OLK14 files are saved in the corresponding profile identity folder to which it belongs. OLK is related to multiple profile components and is not limited to just keeping a copy of messages temporarily.

What is OLK File Format?

The Outlook for Mac was released as a part of MS Office suite 2011 edition that was introduced especially for Mac OS. The client make use of the backend OLK14 MESSAGE file for when a message is read on the client end by the user. The OLK file format only saves the corresponding message header data.

Apart from this, there is another different OLK14 MSGSOURCE which contains the content of email message with no attachment (if any).

Note: Attachments get stored in different OLK format separately.

OLK Folder: It is a folder that is temporarily created on Windows OS by MS Outlook email app. The folder contains all the temporary attachments saved by the client of representing user profile emails. No OLK15 files are created on Outlook for Windows. And name occurs, the folder contains temporary attachments saved copies. However, in some scenarios the attached files don’t reside in a folder for temporary duration but also stays until you purposely delete them.

Default Folder Location of OLK File Format

Mac Outlook 2016

/Users/Library/Group Containers/UBF8T346G9.Office/Outlook/Outlook 15 Profiles/Main Profile/Data/Message Sources

Mac Outlook 2011

/Users/username/Documents/Microsoft User Data/Office 2011 identities/

Variants of OLK File Format of Mac Outlook

Till now, we have only concentrated on storing the message in OLK14 file and also storing the message header in OLKs too. However, there is not just only one or two but number of OLK files produced by Outlook for Mac client version.

Further, the messages are divided to multiple components that are all saved with unique OLK extension. Different variants of OLK file format are mentioned below that can be used to read and extract OLK file data.

Category File:

Category is used to tag messages, contacts, calendars, or such components. The file includes name & color assigned to the category. One cannot easily open or view OLK file format saved by a user. In OLK file you can only read the category as the application is generated as a readable file. Some default categories included in the file are: Family, Personal, Holiday, Categories etc.


[user]/Documents/Microsoft User Data/Office 2011 Identities/Main Identity/Data Records/Signatures/

Calendar Event:

The .olk extension of Outlook for Mac allows to store events data using Outlook calendar. Such type of event include the information like time, invitees, date. Calendar Event OLK15 is used to store local cache copy of created events in the cases when calendar is remotely preserved.


[user]/Documents/Microsoft User Data/Office 2011 Identities/Main Identity/Data Records/Events/

Contact File:

The OLK contact file contains information related to contact details like name, email address and business information. This information is entered in Outlook interface and used to save a contact. Once OLK14CONTACT is created by Outlook, then no direct interactions is made by users.


[user]/Documents/Microsoft User Data/Office 2011 Identities/Main Identity/Data Records/Contacts/

Email Message:

Email message file is represented as OLK14MSGSOURCE that contains email source data for message reference. The application will load the file when one wants to view the particular message. Keeping message and its source separately makes the client function efficiently.


[user]/Documents/Microsoft User Data/Office 2011 Identities/Main Identity/Data Records/Messages Source

Group File:

The group OLK file of Outlook for Mac is created to store the collected group contacts. This is done to maintain collection of contacts in a managed way by the client.

Message File:

The message file of Outlook for Mac i.e. OLK14MESSAGE file stores only the header related details. The application supports this file to read message details like only the header data and not the mail body data. The proper message overview can be taken on the application front-end by the users, with this file loaded by the client on the backend. One can read the file in fragments (of text) by making use of Apple supported text editor.


[user]/Documents/Microsoft User Data/Office 2011 Identities/Main Identity/Data Records/Messages/

Signature File:

Outlook for Mac stores email signature in HTML code form in OLK file format. Therefore, OLK file is saved and loaded by Mac Outlook app automatically and is inaccessible by users via direct means.


[user]/Documents/Microsoft User Data/Office 2011 Identities/Main Identity/Data Records/Signatures/

Mail Account:

The content of mail account in OLK file consists of account setting of configured profile, login details and connection. The file is meant to store account related details that allow users to get emails and synchronize calendar.


[user]/Documents/Microsoft User Data/Office 2011 Identities/Main Identity/Data Records/Mail Accounts/

Preferences File:

These files are represented as OLK14PREF to store software related choices that identify the settings for reading and composing messages. Being application generated are readable files, these OLKs are again inaccessible to software.


[user]/Documents/Microsoft User Data/Office 2011 Identities/Main Identity/Data Records/Preferences/

Note File:

OLK file for Note storage consists of note that was created with the help of Notes component provided in Outlook.

Note: Being generated in binary formatting too, these files contains few fragments in text formatting. This makes .olk file readable to some extent with text editors.


[user]/Documents/Microsoft User Data/Office 2011 Identities/Main Identity/Data Records/Messages/

Task File:

The OLK of task file carries ‘To-do’ created by the user on the application. The information represents the marking applied on messages flagged for the purpose of follow-up. The OLK14TASK is auto-generated as soon as new task is assigned by the user.


The information is provided so that users will be aware about OLK file extension. These are the backend database files supported by Outlook for Mac. The OLK14 file works on a database and not a data file as Windows counterparts. So, the database need files to support reading content when user request the application for implementing many functions like read (emails, calendar, notes etc.) We have discussed the variants of OLK format and how they are linked to the other file by means of file structure in which they are saved. Along with this, the database file residing in the Main Identity folder is also used for the purpose. There are number of amazing benefits of having OLK15 file in spite of database. Removing or relocating any of the OLK15 messages does not result in any blunder as reconstructing the database will reorganise these files at their specific folders.