Redirect mail to a shared mailbox subfolder

Julian12 

Hi, you can add rules to a shared mailbox as shown in the following - https://support.office.com/en-gb/article/add-rules-to-a-shared-mailbox-b0963400-2a51-4c64-afc7-b816d737d164

I'd personally not do it this way though and I'd keep the same number of Shared Mailboxes.  There is no reason to specifically reduce the number of Shared Mailboxes in Exchange Online as you do not require licences for these mailboxes.

As for the second question, there is no direct way to migrate public folders to shared mailboxes.  You can do a public folder migration though or setup public folder coexistence within your hybrid environment.

https://docs.microsoft.com/en-us/exchange/collaboration/public-folders/migrate-to-exchange-online?view=exchserver-2019

https://docs.microsoft.com/en-us/exchange/collaboration-exo/public-folders/set-up-modern-hybrid-public-folders