Is your feature request related to a problem?

Shared mailboxes are a standard IMAP feature, and the container setup doesn't make it easy to configure this feature.

Describe the solution you'd like

Minor restructuring of config files, so users can add a shared mailbox setup by providing additional configuration content or defining env variables without having to alter existing configuration.

Who will that feature be useful to?

Enterprisey setup are likely to benefit from this.

What have you done already?

I have modified existing configuration, and got a shared mailbox setup working.

What are you going to contribute?

If this feature is appreciated, I can contribute changes that are needed, I will just need feedback and review.