A few ISPs don't accept messages sent from a residential IP address. A residential IP address is the one any DSL, cable or modem users get when connecting to the internet. That means they don't accept e-mails from users using their own SMTP server.
eMail Verifier is like an SMTP server so it uses that IP number to identify itself.
Note that thousands of companies worldwide run their own SMTP server over DSL or cable connections.