SMTP Server reply:535 5.7.3 Authentication unsuccessful

This problem is encountered when configuring the mail server (IMAIL) after the server has been reload. Server configuration before countless times, familiar, how this happened suddenly this problem.

From a single hint, the reason is obvious: SMTP authentication failed. However, Foxmail has chosen the SMTP server to verify the options. Previously Foxmail has this bug, but other servers are normal, so be sure, not foxmail problem. The problem can only be found on the IMAIL server.

Trying to turn off the "Send Authentication" option in the IMAIL-SMTP security settings is still the same problem. This is a bit out of the ordinary. Further use IMail's own client tools to test and send and receive normal. That's not IMail's problem.

What could be the problem? Strange things are happening every year, but I don't superstitious. Pour a cup of tea, concentrate on the heart, carefully think of Mail's work process, where can go wrong. The most likely is the port problem, is there any program that takes up 25 ports. In the heart suddenly gedeng a moment, immediately open IIS to look at, sure enough. The default SMTP server is running.

Used to install the server, the useless things have been removed, including SMTP, this time because of the tension, almost all of the default configuration, the result is naturally IIS configured SMTP. Turn off the SMTP default service for IIS, and everything is back to normal. Solved, very simple, summed up, two points:
Microsoft's stuff is strong and overbearing. There is a reason for the fruit, not superstitious or right.