Building API-based email threads for marketplaces: useful or over-engineering?

Hi everyone,

I’m validating a small SaaS idea and would really appreciate candid feedback from people who’ve built marketplaces or peer-to-peer platforms.

Many marketplaces need buyer <-> seller communication, but they don’t want to:

• expose users’ real email addresses
• build and maintain a full messaging/chat system
• force users into another inbox

Large platforms like Airbnb, Upwork, Craigslist, and Turo solve this with email relay infrastructure: users receive messages via email and can simply reply, while real emails stay hidden.

Email is still the lowest-friction communication channel, but building this infrastructure internally can be non-trivial for smaller teams.

So I built a prototype called RelayCore.

The idea:

Developer creates a thread via API -> RelayCore generates a masked email alias -> participants communicate via normal email while identities remain private.

No chat UI. No separate inbox. Just infrastructure.
Think of it as Airbnb style reply-to-email messaging available via a simple API.

Landing page:
https://www.relaycore.io/

I'm trying to validate a few things:

1. Is this painful enough that companies would actually pay for it?
2. Who typically owns this problem (CTO, Product, Trust & Safety)?
3. Do most teams just build something like this internally anyway?
4. If you were building a marketplace today, would you:
   • A) expose emails
   • B) build messaging internally
   • C) use something like this

Brutal feedback very welcome, especially from people who’ve built marketplaces or messaging systems.