Draft email replies in Fastmail with OpenAI

Draft email replies in Fastmail with OpenAI

An n8n workflow that watches a mailbox over IMAP for new unread email. For each one it asks OpenAI to write a short, casual reply in
the sender's language. It then saves the reply as a draft in the Drafts folder of a Fastmail account, filed under the original
message. Nothing is sent. You read each draft, edit it and send it yourself.

What is inside

• workflow.json: the workflow as n8n exports it, eleven nodes: nine that run and two sticky notes. It holds no credential.
• README.md: these notes.

What we changed from the original copy

• The credential links on the IMAP, OpenAI and Fastmail nodes were removed. Select your own.
• The model is now gpt-6-luna, in place of gpt-4o. See "Good to know" for the dates.
• Email Trigger (IMAP) is now version 2.1. Version 2 with the mail left unread re-reads every unread email each time a new one
  arrives, so old mail would get a second draft. Version 2.1 has a "Fetch Only New Emails" option, on by default, which stops that.
• The to field in gather data for draft email no longer fails when an email has no Reply-To header, or one without angle
  brackets. It takes the Reply-To address when there is one and the sender otherwise.
• upload draft email builds its request body with JSON.stringify. The original pasted the reply into a JSON text by hand, so a
  double quote in the reply or in the subject broke the request.
• That body also removes the angle brackets from the message id before it goes into inReplyTo and references. The JMAP mail
  specification (RFC 8621, section 4.1.2.5) lists message ids without them.
• The two sticky notes no longer say GPT-4, and the prerequisites note now says how to set up the Fastmail token.
• Nothing else. The prompt, the Fastmail calls and the order of the steps are as they were.

Before you start

• An n8n instance, on n8n Cloud or your own server.
• A mailbox you can read over IMAP, with its host, port, user and password or app password.
• A Fastmail account with an API token that has the Email scope. Make it in Settings, Privacy & Security, Manage API tokens.
• An OpenAI API key.

Set it up

1. In n8n, create a workflow, open its menu and choose Import from File. Pick workflow.json.
2. Add an IMAP credential for the mailbox to watch and select it in Email Trigger (IMAP).
3. Add a Header Auth credential. Set its name to Authorization and its value to Bearer <YOUR_FASTMAIL_API_TOKEN>, with your own
   token in place of the placeholder. Select it in Session, Get Mailbox IDs and upload draft email.
4. Add an OpenAI credential and select it in OpenAI.
5. Click Test workflow, then send a test email to the watched mailbox. The trigger reads it, and the rest of the flow runs.
6. Open the Drafts folder in Fastmail. A draft headed Re: and the subject of your test email should be there.
7. When the drafts look right, save and press Publish at the top of the canvas (or Shift+P).

How a run goes

1. Email Trigger (IMAP) waits on the inbox and passes on each new unread email. It also downloads attachments, which no later
   step uses.
2. Get fields from source email keeps the plain-text body, the sender, the subject, the message id and the Reply-To header.
3. OpenAI gets the subject and body with a prompt that asks for a casual reply. The prompt asks for a greeting and a sign-off in
   the language of the email, a thanks when it fits, and the formal "Sie" when the email uses it.
4. Session asks Fastmail for the JMAP session, which holds the account id. Get Mailbox IDs lists the account's mailboxes.
5. Split Out turns the list into one item per mailbox, and Filter for drafts folder keeps the one whose role is drafts.
6. gather data for draft email joins the folder id, the recipient, the Re: subject, the reply text and the message id.
7. upload draft email sends one JMAP Email/set call that creates the draft in that folder, marked as a draft and threaded under
   the original message.

Change the look

• The reply style: the prompt in OpenAI. Change the tone, the sign-offs or the languages there.
• The model: OpenAI.
• Which mail is read: the Custom Email Rules in Email Trigger (IMAP). The default is ["UNSEEN"].
• The mailbox: the Mailbox field of the IMAP trigger, INBOX by default.

Good to know

• Model: OpenAI's deprecations page, read on 12 November 2026, lists gpt-4o-2024-08-06, gpt-4o-2024-11-20 and
  gpt-4o-mini-2024-07-18 with a shutdown on 14 January 2027 and names gpt-6-luna as the replacement. This node has no tools, so
  the swap is a plain model change. gpt-6-luna has a reasoning effort setting that defaults to medium, and this node does not set it.
• Not run: Mindket made no call to Fastmail, OpenAI or a mail server. The changed expressions were run offline with sample
  values. A first test with one email is the real check.
• JMAP answers a failed Email/set with a normal 200 reply that lists the draft under notCreated. Look at the output of
  upload draft email the first time to see that created holds your draft.
• The drafts come from the text of an email anyone can send you. A message can carry text meant to steer the model, so read each
  draft before you send it.
• The subject and the text of each email go to OpenAI. The drafts stay in your Fastmail account.
• Once the workflow is published, the trigger can pick up the unread mail that arrived that day, so a busy inbox can mean several OpenAI calls at once.