<?xml version="1.0" encoding="UTF-8"?>
<configuration>
    <system.webServer>
        <rewrite>
            <rules>
				<rule name="二級目錄301重定向到二級域名" stopProcessing="true">
					<match url="^m/(.*)$" ignoreCase="false" />
					<conditions logicalGrouping="MatchAll" trackAllCaptures="false" />
					<action type="Redirect" url="http://m.123.com/{R:1}"/>
				</rule>
            </rules>
        </rewrite>
    </system.webServer>
</configuration>

Apache (.htaccess)

RewriteEngine On
RewriteBase /
RewriteRule ^m/(.*)$ http://m.123.com/$1 [R=301,L]

location ~* ^/m/ {
	rewrite ^/m/(.*)$ http://m.123.com/$1 permanent;
}