Let suppose we share with full acl controls a mailbox like

shared@example.com with folders INBOX, Sent, Junk, Drafts, Trash

to a set of accounts, such as a@example.com and b@example.com

Each a@example.com and b@example.com have their INBOX, Sent, Junk, Drafts, Trash folders too.

When a@example.com logins to SOGo webmail and mark as Junk a mail of a shared@example.com folder, then that mail should be moved to the Junk folder of shared@example.com and not to the a@example.com Junk folder.
The same should happen for other folders: when a@example.com send a mail using the Identity (From) "shared@example.com", then a copy of the mail should be placed in Sent folder of shared@example.com, and not in Sent folder of a@example.com. When a@example.com delete a mail from a folder of shared@example.com, that mail should be moved to the Trash folder of shared@example.com.

I think this behavoir could be reached if you could allow selection of Junk, Trash, Drafts and Sent folders too into an email identity.

Another possibility, completely different, is to allow login as another user. SASL PLAIN let you to enter the authorization username and the authentication username. So a@example.com and b@example.com could login to the mail account shared@example.com with their own passwords.
I prefer the Identity choice really.

Do you think these features could be developed in SOGo?

Thank you to consider this.