You are trying to send email to a particular recipient domain and the server is responding with: "550 5.7.1 external client with IP address <ip address> does not have permission to submit to this server."

You want to know how to resolve this issue.

550 5.7.1 external client with IP address <ip address> does not have permission to submit to this server.

This is an SMTP response code being returned by the recipient's mail server.

In most cases, this means that the recipient domain's firewall, mail server, or mail gateway is refusing connections from your organization.

You will need to contact the administrator of that domain to determine why their organization is refusing connections from yours.