Possible Reasons for Connection Issues

Answer - C.

The AWS documentation mentions the following on the Simple AD service.

Simple AD provides a subset of the features offered by Microsoft AD, including the ability to manage user accounts and group memberships, create and apply group policies, securely connect to Amazon EC2 instances, and provide Kerberos-based single sign-on (SSO)

However, note that Simple AD does not support features such as trust relationships with other domains, Active Directory Administrative Center, PowerShell support, Active Directory recycle bin, group managed service accounts, and schema extensions for POSIX and Microsoft applications.

For more information on the Simple AD service please refer to the below URL:

The reason why you are not able to connect your on-premise AD Microsoft Exchange Email server with the Simple AD service provided by AWS could be one of the following:

A. The firewall is blocking the necessary ports. This is a possibility because firewalls are designed to block incoming traffic to protect the network from potential security threats. In this case, the necessary ports required for the connection may be blocked by the firewall, preventing communication between the on-premise AD Microsoft Exchange Email server and the Simple AD service provided by AWS.

B. The NACL's are blocking the necessary ports. Another possibility could be that the Network Access Control Lists (NACLs) are blocking the necessary ports. NACLs are used to control inbound and outbound traffic at the subnet level. If the necessary ports are blocked by the NACLs, then communication between the on-premise AD Microsoft Exchange Email server and the Simple AD service provided by AWS may not be possible.

C. Simple AD does not work with many Microsoft products This is not likely to be the reason because Simple AD is designed to be compatible with many Microsoft products, including Exchange Server. However, it is always important to ensure that the products you are using are compatible with each other.

D. You need to implement SSL before using Simple AD with Exchange Server. This is also a possibility because Simple AD requires SSL (Secure Sockets Layer) for secure communication between the on-premise AD Microsoft Exchange Email server and the Simple AD service provided by AWS. If SSL is not implemented, then communication may not be possible.

In conclusion, there could be multiple reasons why you are not able to connect your on-premise AD Microsoft Exchange Email server with the Simple AD service provided by AWS. It is important to investigate each of the possibilities mentioned above to identify the root cause and resolve the issue.