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+# 17. Email cache guideline
+
+Date: 2022-10-04
+
+## Status
+
+Accepted
+
+## Context
+
+The logic of Email cache is complicated to follow by all developers
+
+## Decision
+
+Brief the logic flows to easier in following the changes of cache implementation
+
+- Email Caches of each mailbox will be filled by `ThreadConstants.defaultLimit` items at the first time open this mailbox.
+- `State` of `Email` will be cached at the first time cache is filled.
+- Email Caches of all mailbox will be synchronized by `Email/changes` in the case `State` of `Email` is available in local.
+Only items in cache will be updated by `changes`, other will be ignored
+- After any operations (CRUD with Mailbox, Email), `refreshChanges` is invoked to synchronize the cache
+- To guarantee the single of truth, UI only display the final result which fetches from the cache, does not directly show the result come from the back-end
+
+## Consequences
+
+- Any change to `ThreadRepository::getAllEmail` and `ThreadRepository::refreshChanges` should be updated in this ADR