- Saving Sent Items can be on Shared Mailboxes Only (Converting Mailbox to Shared to Set-Mailbox MailboxName –Type Shared)
Get-Mailbox test2016-4 | Set-Mailbox -MessageCopyForSendOnBehalfEnabled:$true -MessageCopyForSentAsEnabled:$true
User1 do SendAs on Test2016-4 Mailbox
Now in Test2016-4 Sent Items you can see Items being saved. Which is not by default.
Enabling From in Outlook Web Access After Applying SendAs Permission in Shared mailbox delegation properties.
Send As is Saved to SharedMailbox