This has never worked since we got the box, and the manual is somewhat confusing. I can only assume I am not setting this up correctly. Perhaps someone can explain *simply* what I need to do.
We have our own domain name (ourdomain.co.uk) and each of the users has his own ISP and email address, such as email@example.com, the ISP domain there being free-online.co.uk. Each user has been allocated an email address using our own domain name, such as firstname.lastname@example.org.
The problem is that they cannot send email using this email address to anyone other than other users within our domain.
POP Authenticated Relaying is enabled in Server Management -> Network services -> Email -> Advanced.