That depends on the point of the e-mail. You can set up a DTS package
to send e-mails as part of a batch run, but it has nothing to do with
C#. The e-mails are fairlly static and are designed to notify you
when something completes or has problems.
The DTS package can then be scheduled to run via SQL Server Agent.
Alternatively you can have sql server agent act as a task runner and
invoke a batch file, but again it has nothing to do with C#.
If its gotta be ASP.NET then the closest thing you're going to be able
to use is the run process capability which could be used to pop up a
browser window and invoke an ASP.net page, but its not going to be
very dynamic.
In short, it depends on what you want to do. Since SQL Server greatly
pre-dates C#, its not going to be possible to write C# code inside of
a SQL Server object unless there's some new experiemental technology
to enable that which probably wouldn't be very stable or reliable.
There's probably a much easier way to do what you want. I would
suggeest creating a windows service using C# that has its own
scheduler and in turn invokes an ASP page on a schedule, or simple
does whatever the page is supposed to accomplish.