Most agentic email setups start the same way: one shared mailbox, one SMTP credential, and a line in the README that says "don't send anything weird." It demos fine. Then the agents start running on schedules, and three problems arrive at once.
Attribution disappears. When four agents can send from support@, an outbound message has no owner. A bad reply can't be traced to a run, a prompt version, or a task. Structured logs help, but only if identity is part of the send path, and most SMTP wrappers drop it.
Threads collapse. An agent that asks a question needs the answer routed back into the same run. With a shared inbox, two agents replying to the same customer produce a thread where each one sees the other's drafts, and the next turn gets ambiguous context.
Blast radius is global. One inbox means one credential, one rate limit, and one compromise path for every agent you run.
The fix is unglamorous: give each agent its own address and its own scoped key.
agent-7@inbox.yourapp.com -> run 48f2, prompt v12
agent-8@inbox.yourapp.com -> run 51aa, prompt v12
Routing becomes a lookup instead of a guess. Inbound mail arrives already attached to a thread, so the agent's next turn has the exact message it was waiting for:
{
"to": "agent-7@inbox.yourapp.com",
"from": "customer@example.com",
"subject": "Re: invoice 1042",
"threadId": "th_9f2c",
"text": "Confirmed, go ahead."
}
Two details matter in practice. First, a per-agent key should be scoped to that inbox, so a leaked key burns one agent instead of the fleet. Second, inbound parsing should return plain text plus a thread id, not a raw MIME blob the model has to decode. Quoted replies and attachments are exactly where agents waste tokens and invent context.
Volanea implements agentic inboxes this way: an isolated address per agent, scoped API keys, and inbound mail parsed to JSON with thread ids. The free tier covers 1,000 emails a month, enough to run a small fleet before committing to anything.
If you are wiring agents to email, count inboxes before you count tokens. Setup notes live at volanea.com/docs.