Peering with mailbox providers allows Twilio SendGrid to deliver emails more reliably and efficiently by reducing the distance traffic has to travel across the internet. This is achieved through private peering, which enables direct connections between networks without relying on public internet transit. As a result, delivery times are significantly improved, and overall performance is enhanced. Additionally, peering provides greater reliability in case of network failures, ensuring that critical services like APIs continue to function smoothly for customers using cloud offerings from Google, Amazon, or other providers.