Backing up Office 365 user's Exchange Online mailbox for offline review and archiving?

[OneTechBeyond]

What's the best method for me to be able to backup/archive another user's Exchange Online mailbox (including their Recover Deleted Items secondary storage area), without interrupting their access to their active mailbox? I have a user that I need to get a reviewable PST of their mailbox,

[#2]

You can do a content search:

https://docs.microsoft.com/en-us/microsoft-365/compliance/export-search-results

Adam

[#3]

Why exactly do you need a backup though? PSTs are unreliable and insecure, I would strongly suggest avoiding them where possible.