outlook not connecting to office 365 server

A deleted or disabled mailbox from the Exchange server.Outlook may fail to connect to the Exchange server due to various reasons, such as: You must connect to Microsoft Exchange at least once before you can use your Outlook data file (.ost). However, when this authentication fails, Outlook cannot connect to the Exchange server mailbox and displays the following or similar error message.Ĭannot start Microsoft Outlook. Although Outlook OST file allows users to work even when the system is offline, it needs to authenticate the user profile by matching the MAPIEntryID GUID key with the server mailbox at least once to allow access to OST and Outlook profile.

This OST file is encrypted with a unique MAPIEntryID GUID key, which is stored in the registry of your local system and Exchange server. Outlook, when configured with Exchange server profile in Cached Exchange Mode, creates an OST or Offline Folder file. Methods to Resolve Outlook Cannot Connect to Server Error.Why Outlook is Not Connecting to Server?.

Outlook not connecting to office 365 server