Support alternate mailaddresses from a users configured e-mail addresses

Short description
I would like to be able to set the e-mail that is used to send an invitation for an event on my calendar.
Since there are multiple aspects and this has things that need to be implemented server side as well as in the calendar app I'm opening the issue here.

Describe the solution you'd like
In an ideal world I would see 2 things happen:

1. In the calendar app or in personal settings allow the configuration of the outgoing e-mail/alias that is to be used automatically.
2. In the calendar app allow the user to chose the from address when creating the appointment.

The reason that (1) is needed is that when using caldav clients they will not have a way to be aware of the e-mail accounts/aliases available to the user on the server.

When (1) is available (2) is a poweruser feature.

As an alternative to (1) what may also be possible is to scan if any of the configured mail addresses has a corresponding MailProvider.

Describe alternatives you've considered
I have tried adding a second e-mail in my personal settings but while it matches the e-mail address that is available it was not used.

Additional context
Specifically for my setup the e-mail address of my user is set by SAML and is internal whereas I have an alias that I prefer to use as well as liking to use unique addresses when I send messages to companies etc, also I can't change said e-mail address.

I have been looking at the code and am now sanity checking myself based on my understanding and hoping for some feedback/brainstorming before I start hacking away.

current flow

1. Appointment with an external party is created in calDAV client (calendar app, thunderbird, gnome calendar, phone app etc.)
2. calDAV backend determines if the user has a mailprovider that matches the e-mail address configured in their user settings
3. If (2) send using that mailprovider
4. If not (2) send with system mail settings if they exist (eg. noreply@domain)

Start by tracing the current CalDAV invitation flow and how configured user e-mail addresses and MailProvider matches are handled. Compare that flow with the requested alias selection and fallback behavior; done means supported aliases can be configured or selected and invitations use the intended sender, including from CalDAV clients.