What is an SMTP server and how does it work?

MPP affects personalization that relies on open-time data like real-time location, current time, or live inventory counts. When Apple's proxy pre-fetches content, any dynamic elements render at that moment rather than when the recipient actually views the email. Location-based content shows proxy server locations, countdown timers display wrong times, and live inventory may have changed by actual viewing.

The impact varies by personalization type. Merge fields populated at send time work fine since they're baked into the email before delivery. Segment-based content targeting also works because it's determined before sending. Only elements that depend on the specific moment of opening face MPP disruption, and these represent a subset of personalization techniques.

Workarounds include shifting dynamic content to landing pages where you control the viewing context, using click-triggered personalization instead of open-triggered, and providing fallback content that makes sense regardless of timing. Some dynamic content providers have developed MPP-resistant techniques, though these continue evolving as Apple's system changes. Effective personalization was always more about relevance than real-time gimmicks; MPP just emphasizes that truth.