Slack · api · fg-0354

Burst of chat.postMessage calls to one channel drops messages or returns ratelimited

ratelimited with a Retry-After header

Verified 2026-10-15 · Confirmed by 0 builders · Trust 50/100

Cause

Posting is limited to about one message per second per channel plus a workspace-wide cap. Slack tolerates short bursts but may not store or display messages past the limit.

Fix

Queue outgoing messages per channel at one per second, honor Retry-After, and batch updates into one message where possible.

Apply

from slack_sdk.http_retry.builtin_handlers import RateLimitErrorRetryHandler
client.retry_handlers.append(RateLimitErrorRetryHandler(max_retry_count=3))  # resends after Retry-After
for msg in queue[channel]:
    client.chat_postMessage(channel=channel, text=msg)
    time.sleep(1)

Affects: Slack Web API chat.postMessage and incoming webhooks, as of 2026-10

Sources

• https://docs.slack.dev/apis/web-api/rate-limits/
• https://docs.slack.dev/reference/methods/chat.postMessage

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