Apple is now working on an issue with the Mail app that surfaced after the update for iOS 11 was rolled out. The problem involves Microsoft email accounts being prevented from sending or replying to emails.

Users with Outlook, Office 395, or Exchange 2016 email accounts are being blocked by the native Mail app. When a user tries to send a message, an error message pops up, saying "Cannot Send Mail. The message was rejected by the server."

Shortly after the official launch of the mobile operating system's newest version, Apple published a support document acknowledging the issue. The company also shared its effort in correcting the problem. "Apple is working closely with Microsoft to resolve the issue and will release a fix soon in an upcoming software update," read the post.

On the same day, Microsoft also published a page describing the problem. "This issue occurs because the Mail app on iOS 11 is not compatible with Outlook.com, Office 365, or Exchange Server 2016 running on Windows Server 2016," said Microsoft in the support document.

Microsoft recommends users to download the free Outlook for iOS client from the App Store, as that app fully supports Outlook, Office 365, and Exchange Server 2016 email accounts.

Bugs like this one are likely to occur whenever there is a new update on the software. However, avoiding them is the reason why companies perform beta testing before releasing official updates.

It sounds like both Apple and Microsoft were caught by surprise with this issue, and it is quite unexpected that Apple would miss this problem even after weeks of beta testing. According to one user who participated in the beta program, he has flagged Apple about the issue way back in July.

Since Apple has not released a fix for the problem, users will have no choice but to use third-party apps compatible with their email accounts, and wait until the company rolls out another update to fix the problem.