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Fastmail

Actions for Fastmail messages, labels, drafts and threads

Actions30

Thread → Reply to a Message

AI-generated

Summary

Reply to a Fastmail message, optionally creating a draft or sending immediately with customizable recipients, subject, and bodies.

Inputs

  • replyMessageId (required) — Message ID within the thread to reply to.
  • to (required) — Comma-separated recipient emails.
  • identityId (required) — Chosen identity (email address or ID) used as the From address for the reply.
  • replyIdentityMode — Select whether to use the selected identity or match the original recipient.
  • autoFillReplyRecipients — Automatically reuse reply recipients from the original message.
  • subject — Reply subject; auto-filled from original if enabled.
  • textBody — Plain text body of the reply.
  • htmlBody — HTML body of the reply.
  • composeOptions — Additional compose settings including CC, BCC, Reply All, Create as Draft, and attachment binary properties.

Output shape

object

Returns a JSON object describing the reply outcome; includes fields such as replyMessageId, submitted, draftCleanup, and uploadedAttachments. When debug is enabled, a debug object with before/after state is included. If Create as Draft is set, only draftId and uploadedAttachments are returned; otherwise success and replyMessageId are included. Errors are thrown unless continueOnFail is enabled.

Examples

Example 1: Send an immediate reply using the selected identity and auto‑filled recipients.

replyMessageId = "12345", to = "alice@example.com", identityId = "selected", replyIdentityMode = "selectedIdentity", autoFillReplyRecipients = true, createAsDraft = false

Example 2: Create a draft reply and attach a binary file from a property.

replyMessageId = "12345", to = "bob@example.com", identityId = "selected", replyIdentityMode = "matchOriginalRecipient", createAsDraft = true, attachmentBinaryProperties = "file1,file2"

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