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what is the final version of ios 11
The final version of iOS 11 was iOS 11.4.1.
when was ios 11.4.1 released
iOS 11.4.1 was released on July 9, 2018.
how did the version 11.4.1 improve iOS
iOS 11.4.1 improves reliability of syncing mail, contacts and notes with Exchange accounts.

Question: what did the version fix
Self-contained rewrite: what did the version 11.4.1 of iOS fix