Exporting mailbox to a PST File
Note: Must have the “Mailbox Import Export” role assigned
From powershell, type New-MailboxExportRequest -mailbox testmbox -name -filepathservernamepstfilestestmbox.pst
This will export all folders and data in each and export it into the specified PST file. Also note that the dumpster will also be exported by default.
If you want to get additional details about the mailbox export request, you can use the Get-MailboxExportRequest or Get-MailboxExportRequestStatistics cmdlet.
if the export fails to complete, you can add -baditemlimit for eg
New-MailboxExportRequest -mailbox testmbox -name -filepathservernamepstfilestestmbox.pst -baditemlimit 50