Account delegation

[ChristophWurst]

Is your feature request related to a problem? Please describe.

As a Nextcloud Mail user I want to delegate my full account to another Nextcloud user. This allows them to act on behalf of me. This feature could be used for assistants and vacation replacements.

Describe the solution you'd like

Add a UI to pick other users as delegatees. These users will then see my account in their left sidebar, and use it as if it were their own. That means they can send emails under my name.
For transparency it should be somehow indicated that it was acted on behalf of someone else.

Work packages

• Account delegation
  • UI for delegator (delegate, list, undelegate) feat: add delegation frontend #12698
  • Backend for delegation feat: add delegation backend #12605
  • UI for delegatee (indicator that an account is delegated) feat: add delegation frontend #12698
• Audit log (for protocol when acting on behalf) Backend for delegation feat: add delegation backend #12605

Describe alternatives you've considered

• Sharing accounts with other users and groups #572

Additional context

• This is the Mail equivalent of Calendar delegation calendar#2706
• 🤝 Unified sharing across apps (if supported by the app) server#51803 could become relevant

[kra-mo]

The main UI for adding a delegate could look like so:

• There is no placeholder if no accounts are delegated. The context is enough.
• The tooltip for the X button is "Revoke access".
• When the X button is clicked, a confirmation dialog appears: "Revoke access? {email address} will no longer be able to act on your behalf" with the options "Cancel" and "Revoke".

When clicking "Add delegate", the following dialog appears:

Then, after selecting someone, the user receives an email informing them about the delegation.

Delegated mail accounts would show up similarly to other accounts for the delegatee, but they would have the subline "Delegated" in Mail settings.

If there are more requirements, like custom permissions, etc., please tell me :)