Correctly use shared mailboxes

Hello,

I'm part of the IT department of a pretty big company (1k+ employees in total), and we are trying to ease our life with the mailbox setup process on the computers.

We have recently found the "shared mailboxes" thing and delegations and tried that for our department mailboxes (ie. email address removed for privacy reasons, email address removed for privacy reasons, ...). It's great that it adds automaticaly the mailboxes to Outlook without us having to type a password, but there are still parts we need to do manually or things that are impossible that way :

 - Shared email doesn't automaticaly appear in "From:" menu when typing an email. I know you "just" have to add it via the "Other address" option, but it's time consuming and explaining employees how to do it is a No because most of them they wouldn't (want to) understand anyway.

 - Emails sent with the shared email are being stored in the "Sent items" folder of the users email (If I send an email with email address removed for privacy reasons it'll be stored in the "Sent items" folder of email address removed for privacy reasons). Again, I know you can change that in regedit but once again, time consuming and we can't think of pushing the reg key through AD because not all our agences have one.

 - You can't preselect a signature for the shared mailbox (With a mailbox added the "normal" way, you can set in the option that when you switch to email address removed for privacy reasons it'll automatically insert/update the signature in the email body), the mail account doesn't appear in the list. This is blocking because we sometimes send communications where we don't want our name to appear but the department so it gives it a more "official" impression.

We have stopped using that because of these reasons but on the left hand we now have to manually install each mailbox when somebody uses a new computer..

Could you give us some advices ? How do you do in your own company to solve these issues ?