There are currently four user preferences for Muting another user:

• Local Email mute
• Local Notifications mute
• Global Email mute
• Global Notifications mute

This bifurcated (quadfurcated?) situation places a cognitive burden on our users, many of whom don't understand the concept of local-vs-global relationship in the first place. While cross-wiki harassment is not common, we owe it to our users to protect them and to have our "Mute" features performs as expected — to prevent unsolicited communications from known parties.

There are a few things that can be explored for these preferences:

• T167902: Build a unified, cross-wiki Mute feature for multiple types of on-wiki and email communication would provide some value but it would be a somewhat expensive venture.
• Add help text to the local preferences to point people to global preferences (caution: this is just more cognitive load.)
• Display the global preference on the local preference page.
• Only allow global preferences for these mute lists, and display help text on the local preferences to point people to global preferences.

You'll also need to consider:

• Migrating the lists
• How new, contextual entry points (e.g. T218265, T218266, T218270) store the preference: locally vs. globally

T216185: Analyze use of mute preferences should also illuminate any decision made here.