We have Cisco IronPort AsyncOS 9.7.0 and we configure the device to do not support TLS.
Starting from yesterday we figured out that we did not have the ability to receive mails from three domains and one of this domains is cisco.com although we can receive mails from other domains successfully.
When we searched for the affected mails by the message tracking we found that we did not have any mails from these domains and also when we searched for the affected mails in the device logs we did not find anything related to them whether domain name or IP address.
Also be informed that when we did MX lookup test for our domain by mxtoolbox.com site we found the following message in the Session Transcript
550 #5.1.0 Address rejected. [813 ms]
Best regards
Mohamed Abdelaty