I was recently trying to check if IIS's SMTP sever was working correctly. To help I turned on the logging, leaving the default "W3C Extended Log Format" selected. I sent the test email and checked the log - to say it was unhelpful is an understatement! I was wrongly assuming that "extended" format meant it would have more information than the other logging formats which didn't have "extended" in their name!

Enter Steve who suggested I change the format to Microsoft IIS Log File Format (shown in the image below). I did, and the log file was suddenly completely what I was expecting and I could straight away see what I needed (the 'TO' email address in this case).

The above principle also works for normal web site logging to!