| Yes, the user is using a different ISP when trying to log into our email
| provider.


Many ISPs will not let you use another ISP for SMTP on port 25, unless they
authenticate. Even then, many will still not, unless there is an
alternative SMTP port, such as 587, or 2525, which also must be
authenticated.

Thus, the person may have to set up SMTP thru whatever ISP he/she is
temporarily using.

Tom