You can check the SMTP logs to see what happens. Please follow these steps to setup and check SMTP log files. a. Enable SMTP Logs Open Start > Programs > Administrative Tools > Internet Information Service (IIS) Manager. Right click "Default SMTP Virtual Server" and choose "Properties". Check "Enable logging". Click "Properties ..." to check all options. b. Check SMTP Logs You can check the SMTP log files at C:\WINDOWS\system32\LogFiles\SMTPSVC1. c. Understand SMTP logs You can open the log file and check the email logs. The most important field is status code. "250" means ok. Here are the meaning of SMTP status codes. Status Code Description 211 System status, or system help reply 214 Help message 220 Service ready 221 Service closing transmission channel 250 Requested mail action okay, completed 251 User not local; will forward to 354 Start mail input; end with "." 421 Service not available, closing transmission channel 450 Requested mail action not taken: mailbox unavailable 451 Requested action aborted: local error in processing 452 Requested action not taken: insufficient system storage 500 Syntax error, command unrecognized 501 Syntax error in parameters or arguments 502 Command not implemented 503 Bad sequence of commands 504 Command parameter not implemented 550 Requested action not taken: mailbox unavailable 551 User not local; please try <....> 552 Requested mail action aborted: exceeded storage allocation 553 Requested action not taken: mailbox name not allowed 554 Transaction failed