In our network, we have na IBM Lotus Notes server, which handles emails for basedomain.com.
Recently we introduced a new IIS Smtp server just for sending automated emails. The Smtp is configured for a domain subdomain.basedomain.com. The server also has a DNS record for subdomain.basedomain.com
Sending emails outside of our network works fine, however it fails when we try to send an email to email@example.com - the email returns with an 5.3.5 error.
We even tried the SMTPDiag tool to test the connection and it ended OK, it listed the correct end-server for email address firstname.lastname@example.org.
Why doesnt it work when sending real email?