Growing number of iCloud users experiencing Mail delivery errors
Apple appears to be experiencing issues with its iCloud Mail service today, as a growing number of users report receiving a delivery error message from email@example.com for every email received (as pictured above). Most users report still being able to receive emails but also receiving the above error report for each email, while others claim the problem is only happening on specific accounts. An Apple support thread has been started with an increasing number of posters experiencing the same issue since this morning.
Reason: Error in sieve filter: Notify mailto: recipient is not a valid address Action: delivered Status: 2.0.0 (Error in sieve filter: Notify mailto: recipient is not a valid address).