Been building agent workflows that send and receive email for a while now. One of the most common mistakes I see is routing all agent email through a single shared inbox like support@company.com or a team Gmail account.

The problem with shared inboxes

When your agent sends outbound from a shared address, you lose thread isolation. Inbound replies all land in the same mailbox and you have to parse who the original sender was, what conversation it belongs to, and which agent should handle it.

You also hit deliverability issues. If one agent workflow triggers spam complaints, it affects every other agent sharing that domain identity.

The fix: provision a dedicated inbox per agent or per job at runtime. Each inbox gets its own address, its own sending reputation, and its own inbound thread. Replies go back to that inbox only - no routing logic needed.

The basic API call is just POST /v1/inboxes with a username and domain. You get back something like agent-outreach-abc123@yourdomain.com. That address is isolated, has its own send/receive history, and you can delete or deactivate it when the workflow finishes.

What this pattern unlocks:

- per-agent deliverability isolation (one complaint doesn't kill your whole sending domain)

- clean thread tracking (replies map directly back to the job that sent them)

- auditability (you can see exactly what each agent sent and received)

- easy cleanup (delete the inbox when the workflow is done, no residual state)

Happy to share more about how we wire up the inbound webhook side if anyone's building agent email workflows.