Apple’s latest operating system for the iPhone, iPad, and iPod touch brings loads of new features and improvements like a brand new Control Centre, a new file manager app, new layout to the App Store, among other things. But like any other operating system, it’s not without its own set of bugs. Following the global rollout of iOS 11, users have reported facing issues in the Mail app where some email accounts are unable to send messages.

The issue with the Mail seems restricted to email accounts hosted by Microsoft on Outlook.com or Office 365, or an Exchange Server. Sending a mail via any of these accounts may bring up an error message that says “Cannot Send Mail. The message was rejected by the server.” Apple has acknowledged the bug and is working with Microsoft on a fix that will be release with a future software update, according to the company’s support page.

Interestingly, the bug was first discovered by beta testers of iOS 11, and it looks like Apple was unable to fix it before releasing the final build. For now, users facing the issue can either log in through a Web browser such as Safari, or can download the standalone Outlook app from the App Store.

Another iOS 11 issue that has been making some noise recently is related to the new Control Centre that does apparently does not fully turn off Wi-Fi and Bluetooth when toggling the buttons. However, unlike the email issue, Apple says that this is not a bug and is intentional so that users can continue to connect their iPhone or iPad for AirDrop, AirPlay, Apple Pencil, Apple Watch, Hotspot, and Location Services in the background.