Hi @morad anand ,
Did you configure the receive connect as open relay?
You could try the following steps.
On the receive connectors that have Anonymous in the PermissionsGroups property, change the RemoteIPRanges property to the list of IP addresses you want to allow to be able to send internally anonymously, such as the servers that route inbound SMTP mail from the Internet.
Here’s a link about anonymous relay for you reference
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