OST or Offline Storage Files represent the user's mailbox data in offline mode on the local machine upon registration with Exchange Server using Microsoft Outlook. It is automatically created on the first use of Microsoft Outlook upon connectivity with the server. Once the file is created, the data is synchronized with the email server so that it is available offline as well in case of disconnectivity from the email server.
A GIF or Graphical Interchange Format is a type of highly compressed image. Owned by Unisys, GIF uses the LZW compression algorithm that does not degrade the image quality. For each image GIF typically allow up to 8 bits per pixel and up to 256 colors are allowed across the image. In contrast to a JPEG image, which can display up to 16 million colors and fairly touches the limits of the human eye.
You can also convert OST into many other file formats. Please see the complete list below.