Send-as and Send-on-behalf of for groups in Outlook

What is the expected behaviour for Sent Items in the 'Send As' scenario? As 365 Groups use a 'conversation' structure, there is no location to save Sent Items to. Thus, taking the example above, all members of the Billing department would hold Sent Items in their own mailboxes leaving no shared 'sent trail'. I'd been exploring 'Send As' with this exact requirement on finding that using an Outlook 2016 profile connected to two 365 subscriptions with 'Send As' rights for several Shared Mailboxes on each, Sent Items directed specifically to the Sent Items folder of a Shared Mailbox would be saved to the Sent Items of the Default 365 Account. (If not specified it is saved to the Sent Items folder of the sending subscription account.)