OSTOutlook Offline Storage File
OST or Offline Storage Files represent user's mailbox data in offline mode on local machine upon registration with Exchange Server using Microsoft Outlook. It is automatically created on the first use of Microsoft Outlook upon connectivity with 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 email server.
EMLE-Mail Message File
EML file format represents email messages saved using Outlook and other relevant applications. Almost all emailing clients support this file format for its compliance with RFC-822 Internet Message Format Standard. Microsoft Outlook is default software for opening EML message types. EML files can be used for saving to disc as well as sending out to recipients using communication protocols.