diff --git a/README.md b/README.md
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@@ -1,3 +1,11 @@
 # Nothing Mail
 
 A temporary email service
+
+## TODO
+
+ - Use an DB other than sqlite. it is not good for concurrent operations.
+ - Do not store the raw mail data in the DB, maybe use block storage (the provider can be a disk provider at first)
+ - Use `bluemonday` to sanitize the mail html before rendering
+ - Cache subject parsed from email. Then when listing the email it is not necessary to parse all mails and retrieve them.
+ - Cache in general?