Error #103 means eMail Verifier was unable to resolve the address that was specified. A prime example of this would be a mistyped IP address, or a domain name of an unknown or unreachable host.
Note that if you get a lot of errors of that kind it may be because port 25 is blocked by your Internet provider. As a result eMail Verifier can check the syntax of the e-mail addresses and whether the domain they belong to exists but the last step, connecting to the address MX Exchanger, can't be performed. You can try to contact your ISP and see if they can remove that block. You will find more information on this here: