RFC: agent@domain.tld as a standard A2A address

[arndcubert]

I'm wondering whether this has already been discussed.
Every organization already operates one globally interoperable transport: email. Would it make sense for A2A to support SMTP as an optional transport, with a well-known mailbox such as agent@example.com similar to how RFC 2142 standardized role mailboxes like postmaster@, hostmaster@ and abuse@?

This wouldn't replace HTTP. An email could simply contain an A2A payload, or even just return an HTTP endpoint or Agent Card to continue the conversation over HTTPS. SMTP would become another transport option rather than a competing protocol.

Could Agent Cards advertise a mailto: endpoint, or is this direction incompatible with A2A's architecture?