URL Rewrite Module Configuration Reference | Microsoft Learn[
^]
The default pattern syntax for
<match>
is a JavaScript-style regular expression. Your rule will match any URL which contains the string
mypage
. Since the URL you're redirecting to includes that string, that URL will also be redirected.
If you want to redirect requests where the path starts with "mypage", then use an anchor:
<match url="^/mypage" />