The default retention period for deleted items (those you can recover by using "Recover Deleted Items" in Outlook) is 14 days, but it can be changed; however, this is a per-mailbox setting, and it needs to be changed using PowerShell, because there is no GUI setting for it. It's easy enough to do this for all existing users, but then this process will need to be repeated anytime a new user is created.
Is there any way to globally set the default deleted item retention period in Exchange Online, so that it's automatically applied to new mailboxes?
(I'm tagging the question with
Exchange-2013 too, since that's what Exchange Online is (currently) based on, and the question also applies to the on-premise edition.)