Gmail Image Proxy

Gmail's image proxy (also called Google Image Proxy or Googlebot-Image) is a system Google uses to cache and serve email images through Google's own servers rather than loading them directly from the publisher's ad server. When a Gmail user opens an email, Gmail fetches images through its proxy — this means the email client that reaches MailAdx is Google's proxy, not the subscriber's device directly. This creates a challenge for open-time ad serving: without special handling, Gmail's proxy can cache the image (serving the same ad to multiple re-opens) and may strip the per-subscriber hash from the URL. MailAdx includes Gmail-specific nonce (random number) handling to force a fresh auction on each open, bypassing Gmail's caching and ensuring accurate per-impression delivery.