Microsoft Azure - Outbound SMTP connectivity
SMTP connections (on TCP port 25) are blocked by the Microsoft Azure platform.
Even as a Cloud Service Provider (CSP), we cannot enable or contact the Microsoft Azure support to request a configuration override in Azure subscriptions.
This configuration is in place to prevent spam and protect the reputation of Microsoft Azure IP addresses.
It is strongly recommended to use an authenticated SMTP relay service and/or a different port for SMTP connections.
For more information, please refer to the Microsoft documentation: https://docs.microsoft.com/en-us/azure/virtual-network/troubleshoot-outbound-smtp-connectivity