Sometimes you cannot send out emails with Microsoft local SMTP Service (127.0.0.1) in your ASP.NET codes.
You can check the SMTP logs to see what happens. Please follow these steps to setup and check SMTP log files.
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.
You can check the SMTP log files at C:\WINDOWS\system32\LogFiles\SMTPSVC1.
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 |
