You received this email because some of your Strava activities are set to ‘Everyone’ – which means they're visible by the Strava community and eligible for achievements like KOMs/QOMs/CRs/LCLs. If you change an activity's privacy settings to ’Only you’ or ‘Followers’, they will no longer appear on public segment leaderboards.
To review your privacy preferences, go to Settings > Privacy on strava.com, and Settings > Privacy Controls in the app. To learn more about privacy settings visit this article.