---
id: "0003"
date: 2026-03-05
status: Accepted
supersedes: "0001"
superseded-by:
affected-paths: [lib/relay/delivery.rb]
affected-components: [delivery, retries]
---

# 0003 — Retry failed deliveries with exponential backoff, capped at five attempts

## Context

Fixed one-second retries hammered receivers that were already struggling: several endpoints throttle by IP, and back-to-back retries during an outage got our sender IP temporarily banned. The fixed-three-times policy from the earlier decision made outages worse, not better.

## Decision

Failed deliveries back off exponentially — 1s, 2s, 4s, 8s, 16s — and give up after five attempts. Retries are never issued back-to-back or in a tight loop; anything that re-sends a failed delivery must go through this backoff schedule.

## Consequences

Struggling receivers get breathing room and IP throttling is no longer triggered. A delivery can now take up to ~31 seconds to fail over all five attempts, so callers must not assume prompt failure.

## Alternatives rejected

Keeping fixed-interval retries rejected: it caused the IP bans. Immediate retry-until-success rejected outright: it is precisely the pattern receivers throttle. Jittered backoff deferred: single-sender volume does not need it yet.
