Indicate the actual sender in delegation

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

In the case of account delegation. If the delegatee sends a message on behalf of the account owner the receiver doesn't get any indication about who actually sent it.

Describe the solution you'd like

Indicate the actual sender in SENDER field https://www.rfc-editor.org/info/rfc5322/#section-3.6.2

Describe alternatives you've considered

No response

Additional context

For now there's no guarantee that the delegatee has a mail account linked to his Nextcloud account or signed in in the mail app.
to be discussed :

• In case he has multiple accounts linked, add a dropdown in mail settings (signed in accounts in the mail app + linked mail address in the nextcloud account)
• In case of no mail accounts linked, make a requirement for delegatee to have one and retrospectively disable delegations that don't respect it.