Send an Email When an Error Occurs in C# using log4net

Question

Currently my application is using log4net to log errors, the web.config for this is as followed:

<log4net>
    <appender name="FileAppender" type="log4net.Appender.RollingFileAppender">
      <file type="log4net.Util.PatternString" value="../../logs/gateway_%date{yyyyMMdd}.log" />
      <appendToFile value="true" />
      <rollingStyle value="Date" />
      <datePattern value="yyyyMMdd" />
      <layout type="log4net.Layout.PatternLayout">
        <conversionPattern value="%date [%thread] %-5level %logger [%property{NDC}] – %message%newline" />
      </layout>
    </appender>
    <root>
      <level value="DEBUG" />
      <appender-ref ref="RollingLogFileAppenderOutput" />
    </root>
  </log4net>

However, the client now wants each error to be emailled to them.

What is the easiest way to do this, can you do it within the web.config file?

Answer 1

You should use SmtpAppender

<appender name="SmtpAppender" type="log4net.Appender.SmtpAppender">
    <to value="[email protected]" />
    <from value="[email protected]" />
    <subject value="test logging message" />
    <smtpHost value="SMTPServer.example.com" />
    <bufferSize value="512" />
    <lossy value="true" />
    <evaluator type="log4net.Core.LevelEvaluator">
        <threshold value="WARN"/>
    </evaluator>
    <layout type="log4net.Layout.PatternLayout">
        <conversionPattern value="%newline%date [%thread] %-5level %logger [%property{NDC}] - %message%newline%newline%newline" />
    </layout>
</appender>

<logger name="ErrorLogger">
    <level value="Error" />
    <appender-ref ref="FileAppender" />
</logger>
<logger name="EmailLogger">
    <level value="Error" />
    <appender-ref ref="SmtpAppender" />
</logger>

In order to send emails only for an specific error you could do something like this

try
{
  // your logic
}
catch (MySpecificException ex)
{
   // I only send emails for exception of type MySpecificException
   LogManager.GetLogger("EmailLogger").Error(ex);
}
catch (Exception ex)
{
   // Just log to a file for the rest
   LogManager.GetLogger("ErrorLogger").Error(ex);
}