I am very very new to this and just trying to configure SMTP virtual server. I have followed a few threads to get it all running, but the mails are not being delivered. What I have done so far - 1) Install SMTP server. 2) SMTP server Properties General Tab - IP address is set to 'All Unassigned'. Access Tab - Authentication is anonymous access. Everything else is left to Default settings. Delivery Tab - Outbound security is anonymous access. In Advance section, entered the domain name in the FQDN field, and localhost in Smart host field. 3) Created an Inbound Rule for SMTP service to allow connections to Port 25. When I try to telnet, everything works up until the point the mail has to be send. Now, the sender's domain is different to the receiver's domain. Not sure if settings have to be changed to allow that? I had set the Relay restrictions on SMTP server, but because I couldn't send the mails, I thought I might as well make it work without the relay first. The error I see while sending the mail is 451 Timeout waiting for client input. I used to get some other error before when I had Relay restrictions on. Can anyone please point me in the right direction? Please let me know if you need more information. Thanks.