The OAB files are the data files that are mainly associated with Outlook Address Book. It is launched by Microsoft Corporation, which stands for Offline Address Book containing names, e-mail addresses and other information attached to the contact name for MS Outlook Email Client. MS Outlook does not need to have connection with the server to obtain the contact's details. Hence, it is called Offline Address Book where user can retrieve information from local OAB file.
Microsoft Corporation introduced OAB File to store the list of the contacts, which was used in MS Outlook 2010. The OAB file is supported by Outlook Express and Outlook 2016. It is also called Microsoft Outlook Offline Address Book that stores contacts used for Microsoft Exchange Server e-mail accounts allowing offline access.
OAB file extension given incorrectly
The Offline Address Book has the file with .oab extension. Sometimes, the extensions can be misspelled making the file inaccessible and user is not able to retrieve information about the contacts. Some common misspellings are ab, pab, lab, iab etc.