Updated FAQ

FAQ.md

@@ -1335,6 +1335,13 @@ consider switching to a modern provider which supports push messages (IMAP IDLE)
 If your device has an [AMOLED](https://en.wikipedia.org/wiki/AMOLED) screen,
 you can save battery usage while viewing messages by switching to the black theme.
 
+By default auto optimize in the receive settings is enabled,
+which will switch an account to periodically checking for new messages when the email server:
+
+* Says '*Still here*' within 3 minutes
+* The email server does not support push messages
+* The keep-alive interval is lower than 12 minutes
+
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