NuGet: https://nuget.org/packages/log4net.Appender.SmtpAppenderWithSubjectLayout
XmlConfigurator.Configure();
ILog logger = LogManager.GetLogger("logger");
logger.Error("Some error");
<appender name="SMTPAppender" type="log4net.Appender.SmtpAppenderWithSubjectLayout, log4net.Appender.SmtpAppenderWithSubjectLayout">
<!-- ... -->
<subjectLayout>
<conversionPattern value="Local // %p: %date [%c]" />
</subjectLayout>
<!-- ... -->
</appender>
Email subject: Local // ERROR: 2013-05-14 23:58:05,847 [logger]