What is the typical response from an SMTP server after a successful HELO command?

The response from an SMTP server after a successful HELO command is typically "250 OK." This response indicates that the server has successfully acknowledged the HELO command sent by the client.

In the context of SMTP, the HELO command is used by the sending mail server to identify itself to the receiving mail server. A response of "250 OK" indicates that the server recognizes the client’s identification and that it is ready to continue the mail transaction process.

The other responses, while they may seem valid in different contexts, are not the standard response associated with the HELO command. For instance, "200 Success" is not a standard SMTP response, "220 Ready" is typically associated with the server's initial greeting, and "250 Accepted" does not correspond specifically to the HELO command, as it is not a recognized response for this transaction. Thus, "250 OK" is the precise and accurate response expected following a successful HELO command.