Ted Graham posted code for a SmtpClientSmtpAppender that extends the SmtpAppender by using the SmtpClient from .NET 2.0 to communicate over SSL with a mail server:
http://weblogs.asp.net/tgraham/archive/2007/04/20/a-log4net-appender-that-uses-smtpclient.aspx An additional option would be to be to send all the log messages as a file attachment (and/or zipped file attachment) and only include the most recent message in the body of the email.
