CExBackup::backupFile:WriteFile Path=\Temporary_Directory\Backup_ID\SERVER\Microsoft Information Store\Mailbox Store (SERVER)\File: Error Number 0x70: There is not enough space on the disk.
The message suggests that the disk space on the MS Exchange machine has ran out. The disk where spooling directory is located doesn’t have enough space.
Free up some space on the disk.
In order to perform a MS Exchange server backup, it is required for the corresponding machine to have sufficient free space for the spooling of the server file. To resolve the issue, free up some disk space on the local drive so that the disk has enough space to hold the contents of the spooling directory.
Alternatively, you could also configure the temporary spooling of the server file to a network path, however ensure that the network path does not require user authentication.