pub.client:smtp on 4.6

I am using the pub.client:smtp and am sending to an outside account ( for example). I have placed the relay server Ip address in my ‘logging’ settings (10.xx.yy.zz). I do NOT place anything in the ‘mailhost’ parm of the smtp service.

The error I get is “is javax.mail.MessagingException: 501 : domain string is NULL.”. If I put in ‘’ as my mailhost, then I get “ javax.mail.SendFailedException: Sending failed;
nested exception is:
javax.mail.MessagingException: Unknown SMTP host:;
nested exception is:

Is there a setting to identify the ‘Domain’ ???

Any help is appreciated,

You should specify your internal mail server’s ip address in the mailhost parameter. The mailhost parameter is not the host name of the ‘to’ address that you are specifying.

-Rajesh Rao