"PST migration" option not showing in Outlook Enterprise Vault ribbon

there actually is a way to use the clients for exports and imports.

To export you can select folders or mails and click Export to PST, in the Enterprise Vault context menu.

You can also enable to import PST, this is done in the Policy/Advanced Settings something like "Enable Client migration"

But it is usually preffered to use VAC or script the migration via Powershell scripts (Export-MailboxtoPST / Export-EVArchive & Import-EVPSTFile)

PST migration feature is available only through the vault admin console.