Inbox forwarding

Resign inbound mail and send it to an address on a sending domain.

Forwarding sends a copy of each inbound message to another address. PostShiba writes a new message and signs it with your domain, so the copy passes authentication checks at the destination.

How the copy is built

An inbound message's original From may be a domain PostShiba cannot sign for. So the copy is a new message:

Header Value on the copy
From The inbox mailbox at the forward address's domain, such as support@example.com
Reply-To The original sender
X-Original-From, X-Original-To The original sender and recipient
DKIM Signed with the forward address's sending domain

The copy keeps the subject, both bodies, and the attachments. Replies from the destination go back to the original sender.

The copy is sent on your first sending-ready cluster, with an SMTP credential for that domain's tenant. Its delivery webhooks carry the unique args kind inbox_forward, inbox_id, and inbound_message_id.

Set a forward address

The forward address must be on one of your verified sending domains. It cannot loop back to the inbox's own host, and it cannot be another inbox.

  • New inbox. Fill in Forward to on the Issue inbox form, or pass forward_to on API create.
  • Existing inbox. Open the inbox, select the Webhook pill, change Forward to, then select Save webhook. The API has no inbox update, so this change is dashboard only.

Forwarding before approval

Until your team has production approval, forward-to addresses count as allowed recipients, like teammates. See Does PostShiba require production approval?.

Next steps