The message was rejected by the server.” 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 i OS 11: “Cannot Send Mail.The message was rejected by the server.” Again, simply installing the latest release of i OS 11.0.1 (or newer if one appears) should resolve the Microsoft email problems on an i Phone or i Pad.If the device is not recognized by i Tunes, placing it into Recovery or DFU mode and then restoring may be necessary.Some apps are not compatible with i OS 11 because they are 32 bit.
Older devices in particular may experience some sluggishness after installing a more recent software update.
Rarely, an i Phone or i Pad may fail during the actual installation of i OS 11 or another software update.
This is quite unusual, but when it does occur it’s usually pretty obvious in that the i Phone or i Pad will be stuck on an Apple logo screen for many hours without a progress bar, or the device screen will be stuck in some otherwise unusable state with a completely black or completely white screen.
If app crashes persist, sometimes rebooting after installing app updates can fix errant app crashing issues too.
Many users report battery life issues after updating to i OS 11 (or any other software update for that matter).