MessagingException error

["Grizzly M" <grizzlym@xxxxxxxxxxxxxxxxxxxxx>]

Can anyone tell me what would be causing me to get the following error
when using JavaMail?

javax.mail.MessagingException (This returns error code 101).

Could it be because I'm not authenticating to the email server? I was
receiving the error java.net.UnknownHostException

so I changed the host name in my properties file and that was when I
started to receive the messaging exception error. I can't seem to find
any information for this exception.

Thanks.