This stackoverflow question brought to my attention that the mail taks isn't usable with SMTP servers which require authentication.
http://stackoverflow.com/questions/1079293/how-to-make-nant-send-an-email-using-a-real-account
I changed the implementation of the mail task in a way that it is using System.Net.Mail instead of System.Web.Mail.
Since the git repository isn't filled and I don't want to install vcs, I upload the whole file instead of a proper .patch file.
Changed Implementation to use System.Net.Mail with authentication, SSL and user defined ports
In review...
Needs work. The idea makes sense but the main problem with this patch is that it use System.Net.Mail which is only available in .NET 2.0+. NAnt still targets 1.* frameworks.
I will look at this again once 0.91 is final.
Since rmboggs fixed it without taking this patch into account with https://github.com/nant/nant/commit/2f1be53b589e5a648fbbd40f883cf8109dbc0ba4 I think this issue can be closed and marked as fixed.