Send Follow Up Reply

Reply to a follow-up without Gmail, over the chosen transport:

• "domain" (default): SES from the workspace's verified receiving domain, with full threading headers, so it lands in the customer's existing thread and their next reply attributes back by header.
• "resend": the workspace's Resend identity, threading headers included (Resend passes them through).
• "autosend": the workspace's AutoSend identity. AutoSend reserves the threading headers, so the reply arrives as a "Re:" without hard threading; attribution of the next customer reply falls back to the subject match.

The outbound copy is echoed into the message store, which moves the item to Responded. When draft_id is given, the (possibly edited) body is saved back onto the draft before it's marked sent.