Apple's iOS 11.01 seems to have addressed previous problems that prevented users from sending emails from Outlook.com and Exchange accounts along with at least one potentially critical security flaw.
The update was released on 26 September and while Apple doesn't explicitly state the issues the update addressed, a recent Apple support page implied the latest version fixes an iOS 11 issue users experienced when trying to send emails hosted by Microsoft and Outlook.
The email error resulted in a messages that read: "Cannot Send Mail. The message was rejected by the server." Apple instructs users to update to iOS 11.01 or later in order to address this issue.
A US-CERT notification said the update addresses vulnerabilities in previous iOS, some of which could allow a remote attacker to take control of an infected system. Apple is known for not disclosing vulnerabilities until investigation have been conducted and systems are sufficiently patched.