XEP-0033 may be used as a simple metadata marker when sending messages (e.g. to indicate a
`replyto`). The validation was failing on that due to missing `to`, `cc` and `bcc`.
- Code has been rewritten using Pydantic models and `async` coroutines for data validation
and cleaner element parsing/generation.
- Delivery has been completely rewritten. It now works even if server doesn't support
multicast, and send to local multicast service first. Delivering to local multicast
service first is due to bad support of XEP-0033 in server (notably Prosody which has an
incomplete implementation), and the current impossibility to detect if a sub-domain
service handles fully multicast or only for local domains. This is a workaround to have
a good balance between backward compatilibity and use of bandwith, and to make it work
with the incoming email gateway implementation (the gateway will only deliver to
entities of its own domain).
- disco feature checking now uses `async` corountines. `host` implementation still use
Deferred return values for compatibility with legacy code.
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