Is there anything useful in /var/log/qmail/current?
If you use 'putty' to connect to your server (or if you login on the physical console connected to the server) and type telnet maila.microsoft.com smtp do you get 220 mail04.microsoft.com Microsoft ESMTP MAIL Service ready at Sat, 25 Aug 2007 07:49:15 -0700 (or something like it)? (If not, your ISP may be blocking traffic on port 25).
(Note: type "quit" and press <Enter> to close the connection. You may not see what you're typing - don't worry, just type it...)
What happens if you replace 'maila.microsoft.com' with your ISP's mail server in the command above? You should get some sort of smtp id string.
If you have created the actual domain name on the SME server, but are hoping to have the email relayed off-site, you may have a problem - the SME will "swallow" the email, assuming it's destined for itself, and will never send it off-site. Try sending a test message to another domain.
If none of these ideas prove useful you are likely to have some sort of general email configuration problem or upgrade problem. To proceed you would need to tell us:
- exactly how you upgraded from 6.1 to 7.2
- if you did an in-place upgrade, which instructions (or what procedure) did you follow?
- What add-ons had been installed on the 6.1 server? were they removed before the upgrade, or not?
- How was the 6.1 server configured?
- How is the 7.2 server configured?
(It occurs to me that 7.2 by default has the 'smtp proxy' enabled - you might try disabling it under Security::Proxy settings in server-manager).
Good luck; keep us posted!