Apple launched its iOS 11 software update worldwide earlier this week, bringing a slew of new features to iPhone and iPad owners. However, some users should stay well away from the new iOS upgrade, and here’s why:

Microsoft and Apple have both acknowledged a bug in the current release of iOS 11 that causes issues when using Office 365 and the native iPhone Mail app. If your email account is hosted by Microsoft on or Office 365, or an Exchange Server 2016 running on Windows Server 2016, you might see this error message when you try to send an email with iOS 11: “Cannot Send Mail. The message was rejected by the server.” Apple & Microsoft are currently working together to resolve this issue and supporting articles from both companies can be found below:

Microsoft Knowledge Base Article

Apple Knowledge Base Article

At this time, Worksighted Support Engineers encourage anyone who uses the native iPhone Mail app from Apple for communication to delay upgrading their iOS until an solution is in place to resolve this issue. If you or any of your users have already downloaded iOS 11 and are having issues, feel free to contact Worksighted Support. Do not contact Apple or Microsoft about this issue as they are closely together to resolve the issue and will release a fix soon in an upcoming software update.