Daily email deliverability digest in Slack

Build me a code workflow that posts a daily email deliverability digest from Postmark into a Slack channel, Monday through Friday at 9am local time.

Trigger: cron, weekdays at 09:00 in the user's timezone.

Inputs the user should configure at the top of the workflow: the Postmark server to monitor (default to their production server), the Slack channel to post to (default #email-ops), the timezone, and the green/yellow/red thresholds. Defaults: red when hard-bounce rate is above 2 percent OR there are any spam complaints in the window; yellow when the soft-bounce rate is more than 50 percent above its 7-day average; green otherwise.

Steps:

1. Sanity check the Postmark server. Call Postmark's Get Server endpoint and confirm DeliveryType is "Live" (not "Sandbox"). If it is a sandbox server, post a single-line warning to Slack and exit, so we never silently report on test traffic.

2. Pull yesterday's stats from Postmark, for the 24-hour window ending at midnight local time. Use these three operations in parallel, each scoped to the configured server and to the [fromdate, todate] range that covers yesterday:

- Postmark Get Outbound Overview (sends, bounce rate, opens, unique opens, spam complaints, total clicks).

- Postmark Get Bounce Counts (daily and total counts by type: HardBounce, SoftBounce, Transient, SMTPApiError). Bounce rate is (HardBounce + SoftBounce) / Sent.

- Postmark Get Spam Complaints (per-day and total spam complaints).

All three endpoints return the whole window in one call; no pagination needed.

3. Pull the previous day's stats (the day before yesterday) using the same three operations, so we can compute day-over-day deltas.

4. Pull the prior 7 days of stats using the same three operations with a 7-day window ending the day before yesterday, and compute 7-day averages for: total sends, hard bounces, soft bounces, bounce rate, spam complaints, unique opens. This is the baseline.

5. Decide the status. Apply the threshold rules in order: red first, then yellow, then green. Capture the reason string for the status (e.g. "hard-bounce rate 2.4% > 2% threshold") so we can show it in the message.

6. Format a compact Slack message. Use Slack mrkdwn, not standard Markdown. It should have: a one-line headline with a colored circle emoji matching the status (🟢/🟡/🔴), the date the digest covers, and the reason if not green. Below that, a small fixed-width table inside a code block with columns Metric | Yesterday | Δ vs prior day | 7-day avg, with rows for Total Sends, Hard Bounces, Soft Bounces, Bounce Rate, Spam Complaints, Unique Opens. Format percentages to one decimal place. End with a single line linking to the Postmark server activity page for that server, formatted as <https://account.postmarkapp.com/servers/{serverId}/streams/outbound/activity|Open in Postmark>.

7. Post the message to the configured Slack channel using Slack Send a Message.

Edge cases to handle:

- If yesterday had zero sends, skip the threshold logic and post a single calm line: "No sends in the last 24 hours on {serverName}." Do not flag this as red.

- If any of the Postmark calls fails, post a short failure notice to Slack with the error code/message and the server name, so the team notices the digest didn't run cleanly.

- Round all rates to one decimal place. Show counts as integers with thousands separators.

This is deterministic arithmetic and formatting on structured stats data, so build it as a code workflow with discrete nodes, not an agent.