In Zimbra, signatures are an account property and thus must be set up on all accounts the "info@" mailbox is shared to.

If you need for multiple users to send as "info@" you'll need to:

 - Allow all needed users to "Send As" info@ (ZeXtras Suite comes with the "Delegated Authority Settings" free feature - otherwise you'd need to do this via Zimbra CLI.)

 - Add a new "Persona" to each user (in the ZWC: Preferences -> Accounts -> Add Persona).

 - Create the appropriate signature on each user and set it up so that it'll be used as the default signature for the "info@" persona.

Once all steps are cleared, authorized users will be able to choose the sender of any email through a drop-down menu in the compose window.

You can automate the use of the persona in the settings, making it the default address to be used when replying to emails sent to a specific address or when replying to emails contained in a specific folder.

You don't need to share the "info@" mailbox for delegation rights, but doing so allows you to automate the persona as mentioned above. The "Sent" folder management can be done by setting up an Outgoing Filter that will move any item from the "info@" address to the info@ sent.