There are times that you may be asked to export the contents of an Exchange mailbox to a pst. Other times accounts may be being merged and you may need to export the contents of an account being merged and import the mails to the account which will be kept.
Before you begin, your account needs to have the Mailbox Import Export role and you need a folder to export to that the Exchange server has rights to. I like to have a drive on an Exchange server itself to use for the exports. Just make sure the Exchange servers have rights to that folder and you have a unc path - the ones that begin with backslash backslash. (\\)
See here for how to Add the Mailbox Import Export Role to a Role Group
To initiate the export:
New-MailboxExportRequest –Mailbox alias -FilePath \\servername\PST_Export\alias_date_filename.pst
Where alais is the user's alias.
Check status of queued export
To import a pst to a mailbox
New-MailboxImportRequest -Mailbox destinationalias -FilePath \\servername\PST_Export\alias_date_filename.pst -TargetRootFolder "SourceAlias Imported"