Hi, we have an Exchange 2003 server. Our Finance staff have started to email payslips from within software from MYOB.
They found they can email all staff who gave an email address which is on the domain but cannot email to any staff who provided an external email address.
On contacting the support the advice they gave was to change the settings on the Default virtual SMTP server, Relay tab. To select "All except the list below" for computers which may relay through this virtual server.
This fixes the problem but I am not comfortable leaving the setting like this as I'm not sure if this is creating an open relay.
Also 'Allow all computers which successfully authenticate to relay, regardless of the list above' is selected and always has been.