Some users may be unable to send or receive email messages and receive a Non-Delivery Report (NDR)

Title: Some users may be unable to send or receive email messages and receive a Non-Delivery Report (NDR)
User impact: Users may be unable to send or receive email messages and receive a NDR with a 550 or 554 error code.
More info: This issue only occurs if either the sender or user who is receiving the message is utilizing a specific third-party anti-spam service. Senders receive the NDR which states that the message has been rejected due to a 550 or 554 error code, “Remote server returned message detected as spam” error message, and that their host IP address is listed on the third-party anti-spam service.
Current status: We’ve received reports that some users may be unable to send or receive email messages due to a third-party anti-spam service listing our IP addresses within their service. We’re working with the third-party anti-spam service to better understand why our IP addresses have been listed and what actions need to be taken to resolve this issue.
Scope of impact: This issue may affect any user’s mail flow if they’re leveraging a specific third-party anti-spam service to filter email messages.
Next update by: Friday, January 5, 2024, at 11:00 PM UTC