You may face an issue sending emails from your website (PHP or ASP.NET) using the local server SMTP service. In this case, you require to check the SMTP log of IIS. Please refer to the following steps to check the SMTP logs in the Windows Server (IIS).

Enable SMTP Logs

1. Login to your server. 
   
   
2. Go to the Start > Administrative tools.
   
   
3. Click on Internet Information Service (IIS) 6.0 Manager.
   
   
4. Expand your hostname at IIS 6, it will show you SMTP Virtual Server #1.
   
   
5. Right-click on SMTP Virtual Server and click on Properties.
   
   
6. Click on Enable logging and then click on the Properties button. 
   
   
7. At logging properties, click on the Advanced tab and check all the boxes and click on the OK button. 
   
   

Check SMTP Logs

Once the SMTP logs are enabled, we can find all the logs at the below location.

C:\WINDOWS\system32\LogFiles\SMTPSVC1

Understand the SMTP Log

If you find the status code "250" it means ok. Here is the understanding of SMTP status codes.