How do SMTP services handle throttling and retries?

**SMTP** services implement throttling to respect **MBP** rate limits and avoid being blocked. They track how many connections and messages each receiving server accepts, backing off when limits approach and adapting to different provider tolerances.

Retry logic handles temporary failures (4xx responses). Services queue messages, wait increasing intervals (exponential backoff), and reattempt delivery. Typical retry periods span 24 to 72 hours before declaring permanent failure. This persistence handles transient issues without losing messages.

Good services adapt throttling to real-time feedback. If a provider starts rate-limiting, they slow down immediately rather than pushing until blocked. This dynamic adjustment maintains delivery relationships without manual intervention.