· 15 min read
Email to Slack: threading, Block Kit limits, and the duplicate-post trap
Slack's own email-to-channel needs a paid plan, pins every message to one fixed channel, and can't thread. Wiring inbound email to Slack yourself is about 50 lines — but three things bite once real mail arrives: Slack rejects any header block over 150 characters, webhook retries post the same email twice, and Incoming Webhooks never return a message ts, so an email thread can never become a Slack thread. Here's the handler that survives all three, and the return path that lets your team reply to the customer from inside the Slack thread.