I hope someone can shed some light onto thiw. None of the solutions I have found have worked.
A customer has an SBS 2003 server running exchange. They use SMTP for both incoming and outgoing mail.
Someone is sending 1000's of mails through their server as firstname.lastname@example.org
I have tried all sorts to block them but they appear to have random IP addresses. If I disable SMTP relay then nobody can send or recieve mails. If I turn on authentication then outside servers cannot send mail to their mail server.
Hope someone has come across this before.
Thanks in advance