---
title: "Engineering stories behind the Medium Daily Digest Algorithm: Part 1"
description: "Medium’s Daily Digest recommendations were less relevant than the homepage despite identical story sourcing, ranking model, and features, because digest filtering operated with less email-reporting information and was too aggressive. The “Sent in Opened Digest” filter excluded all 15 stories after an email-open signal, even when a reader saw only the first five; Apple Mail Privacy Protection also caused servers to preload messages, making many open events unreliable. Medium removed that filter and reduced the backoff from seven to four days, accepting more repetition while relying on other filtering rules and organic recommendation changes to diversify digests. An A/B test found that experiment users were 10% more likely to convert to paying members and read 7% more on Medium. The post says these results led to more filter investigations, including Bloom Filters, “Hard vs Soft Filtering,” and cross-digest diversification, while recommending audits of products that depend on email-open tracking."
---

# Engineering stories behind the Medium Daily Digest Algorithm: Part 1

[Medium](https://yomu.fyi/company/medium) · Raphael Montaud · Aug 26, 2025

**Type:** Problem & solution

## Summary

Medium’s Daily Digest recommendations were less relevant than the homepage despite identical story sourcing, ranking model, and features, because digest filtering operated with less email-reporting information and was too aggressive. The “Sent in Opened Digest” filter excluded all 15 stories after an email-open signal, even when a reader saw only the first five; Apple Mail Privacy Protection also caused servers to preload messages, making many open events unreliable. Medium removed that filter and reduced the backoff from seven to four days, accepting more repetition while relying on other filtering rules and organic recommendation changes to diversify digests. An A/B test found that experiment users were 10% more likely to convert to paying members and read 7% more on Medium. The post says these results led to more filter investigations, including Bloom Filters, “Hard vs Soft Filtering,” and cross-digest diversification, while recommending audits of products that depend on email-open tracking.

## Context

The Daily Digest and homepage used the same recommendation algorithm, but Digest recommendations were consistently worse. Limited email reporting and aggressive filtering caused stories to become ineligible after an email was marked opened, including stories readers might not have seen. Apple Mail Privacy Protection further inflated open events through server-side preloading.

## Approach / What changed

Medium removed the “Sent in Opened Digest Filter” and reduced the filtering backoff from 7 to 4 days. The change allowed more repetition so strong stories could reappear, while other filtering rules and organic recommendation evolution were expected to diversify daily digests. The team evaluated the change with an A/B test.

## Takeaways

- The Digest contained 15 stories, but an opened-email signal previously made every story in that Digest ineligible for the reader, even if the reader saw only the first few.
- Apple Mail Privacy Protection caused email servers to preload messages, and the post says estimates suggested 50% to 80% of Medium’s email-open events were fake.
- The A/B test showed a 10% increase in likelihood of converting to a paying member and a 7% increase in reading on Medium, with no apparent user complaints about repetition.

**Tags:** [Experimentation](https://yomu.fyi/topic/experimentation), [Privacy](https://yomu.fyi/topic/privacy), [Recommendation Systems](https://yomu.fyi/topic/recommendation-systems)

- Source: [Medium](https://medium.engineering/engineering-stories-behind-the-medium-daily-digest-algorithm-part-1-909a7ca5e807)
- Source URL: https://medium.engineering/engineering-stories-behind-the-medium-daily-digest-algorithm-part-1-909a7ca5e807
- Ingested by Yomu: 2026-09-09T16:02:35.207Z

[Read original post](https://medium.engineering/engineering-stories-behind-the-medium-daily-digest-algorithm-part-1-909a7ca5e807)