I am getting a bounced email like the following:
5.7.1 This system has been configured to reject your mail. An IP address (18.104.22.168) found in the message's 'Received:' headers is listed by the lookup site 'xx.xx.com.'. (in reply to end of DATA command)
The recipient server has some protection that will reject email that contains black-listed IP in the email. These black-listed IPs covered quite some broadband users' IP, so we believed the recipient server has been over-protected in this case.
To overcome this, you'll have to login with VO webmail and send email from there. Since your broadband IP will not be included in the email sent by using webmail, the chances of getting the email out to these recipients are much higher.