Azure Email Communication Service - Sender

Question

I have configured Azure Communication Services and

1. added an instance of Email Communication Service
2. configured a custom domain
3. verified custom domain
4. written some .NET code to send an email

All of the above works, however I would like to understand if it is possible to configure the Email Communication Service above to accept multiple sender addresses or if it is necessary to create an instance for each sender address.

In the azure portal:

It appears that only a single sender address may be set - eg DoNotReply@.

In the client library code, it appears that you can set the sender address:

Sender address set in code

However, if you set this to anything other than that configured in the Azure portal, we see and exception, and that exception indicates a "list" which can be managed by an admin.

So the question is, how can I add further sender addresses to this list eg client1@, client2@ etc?

Exception thrown