Hi all,
I think the DNS is only for internal purpose ... But you could enable a second DNS service for external purposes ... It's explained in "Public DNS Server
HOWTO for E-SMITH 4.1.X" (a contributed How-to, you could find it in the correspondant section on
http://www.e-smith.org).
Just pay attention you musn't do all of what's marked in this How-To because it's especially written for version 4.1.X ... and in fact, you could easyly broke all DNS configurations (in relation with the web-manager).
Personnaly, I've installed already 4 SME servers at my clients, with this kind of "patch" in a custom-template form ... and it works. But I don't know if it is another way to do it better or if it's a marketting choice, and I don't have the skills to do it more efficiently. Don't forget you should have another server to make a backup DNS server ... even if it's not really mandatory for very small entreprises ... and then it's justified to use the commercials services of SME.
Anyway more information is always welcome ...

) ... especially because after this kind of modifications, nothing is anymore linked with server-manager and than all modifications of DNS must be done via SSL for example, in console mode ... (and, I'm so sorry for that, but I don't know how to backup this kind of modifications with all the i-bays ... then after all "real" upgrade, I lost everything ...)
Hope this helps ...