You have your pattern wrong. It should not include domain name or query string there -- only path without leading slash. See the working rule below:
<rule name="MyRewriteRule" stopProcessing="true">
<match url="^(some-file-here)$" />
<conditions>
<add input="{HTTP_HOST}" pattern="^services\.mydomain\.com$" />
</conditions>
<action type="Redirect" url="http://mydomain.webhost.com/folder/{R:1}" />
</rule>
The above rule will only trigger if host name is services.mydomain.com
. If you do not require such additional condition (which is optional) then just remove these 3 lines: <conditions>...</conditions>
Also, the above rule will only do one specific redirect from services.mydomain.com/some-file-here
to mydomain.webhost.com/folder/some-file-here
. If you need to redirect ANY file like that, then use this one instead:
<rule name="MyRewriteRule" stopProcessing="true">
<match url="(.*)" />
<conditions>
<add input="{HTTP_HOST}" pattern="^services\.mydomain\.com$" />
</conditions>
<action type="Redirect" url="http://mydomain.webhost.com/folder/{R:1}" />
</rule>