SmtpAppender fails sending Emails through smtp-server while SmtpClient works

Question

I try to use the SmtpAppender in LogNet:

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

When I enable debug logging in Log4net I receive the following error:

log4net:ERROR [SmtpAppender] ErrorCode: GenericFailure. Error occurred while sending e-mail notification. System.Net.Mail.SmtpException: Failure sending mail. ---> System.Net.WebException: Unable to connect to the remote server ---> System.Net.Sockets.SocketException: An attempt was made to access a socket in a way forbidden by its access permissions (IP from SMTP-Server):25 at System.Net.Sockets.Socket.DoConnect(EndPoint endPointSnapshot, SocketAddress socketAddress) at System.Net.ServicePoint.ConnectSocketInternal(Boolean connectFailure, Socket s4, Socket s6, Socket& socket, IPAddress& address, ConnectSocketState state, IAsyncResult asyncResult, Exception& exception) --- End of inner exception stack trace --- at System.Net.ServicePoint.GetConnection(PooledStream PooledStream, Object owner, Boolean async, IPAddress& address,Socket& abortSocket, Socket& abortSocket6) at System.Net.PooledStream.Activate(Object owningObject, Boolean async, GeneralAsyncDelegate asyncCallback) at System.Net.PooledStream.Activate(Object owningObject, GeneralAsyncDelegate asyncCallback) at System.Net.ConnectionPool.GetConnection(Object owningObject, GeneralAsyncDelegate asyncCallback, Int32 creationTimeout) at System.Net.Mail.SmtpConnection.GetConnection(ServicePoint servicePoint) at System.Net.Mail.SmtpTransport.GetConnection(ServicePoint servicePoint) at System.Net.Mail.SmtpClient.GetConnection() at System.Net.Mail.SmtpClient.Send(MailMessage message) --- End of inner exception stack trace --- at System.Net.Mail.SmtpClient.Send(MailMessage message) at log4net.Appender.SmtpAppender.SendEmail(String messageBody) at log4net.Appender.SmtpAppender.SendBuffer(LoggingEvent[] events)

However. When I try to send a mail through the same SMTP-Server from within my program that uses this log4net-configuration:

MailMessage msg = new MailMessage(sender, recipients, subject, body);
mtpClient client = new SmtpClient("smtp.company.com", 25);
client.Send(msg);

everything works fine. So this could not be a simple SMTP-Server/FireWall-Issue.

Is the SMTPAppender working differently that the standard StmpClient.Send() from .NET that could cause this issue?

If you look at the stack trace, it looks like the SMTPAppender is also just calling SmtpClient.Send. — Bob G

Ole Albers Ole Albers · Accepted Answer · 2017-10-11T13:21:44

@Bob Geiger pointed me into the right direction that Log4net seems to use exactly the same mechanism.

As it turns out this was a Virusscan/Spam-Protection issue. Only defined applications where allowed to send mails through our smtp-server. While one program of us worked which used the same backend as the log4net - application it hat a different filename and so was allowed to send mails, while the other program wasn't.

We had to allow the specific .exe - file in the virusscan-configuration.

SmtpAppender fails sending Emails through smtp-server while SmtpClient works

1 Answers