Am I correct that you haven’t customized any outgoing e-mail settings in your WordPress install? If so, you’ll probably need to explicitly set it to the 20.20.20.20 mail server (the MX record won’t do it). A common way to do that is with the WP Mail SMTP plugin set to “Other SMTP”. You’ll want to include an SMTP username/password if your 20.20.20.20 server requires it.
