diff --git a/src/client/theme-default/support/utils.ts b/src/client/theme-default/support/utils.ts
index 3d05e9f5..1cd168cd 100644
--- a/src/client/theme-default/support/utils.ts
+++ b/src/client/theme-default/support/utils.ts
@@ -21,10 +21,17 @@ export function ensureStartingSlash(path: string): string {
 }
 
 export function normalizeLink(url: string): string {
-  if (isExternal(url)) return url
+  const { pathname, search, hash, protocol } = new URL(url, 'http://a.com')
+
+  if (
+    isExternal(url) ||
+    url.startsWith('#') ||
+    !protocol.startsWith('http') ||
+    /\.(?!html|md)\w+($|\?)/i.test(url)
+  )
+    return url
 
   const { site } = useData()
-  const { pathname, search, hash } = new URL(url, 'http://a.com')
 
   const normalizedPath =
     pathname.endsWith('/') || pathname.endsWith('.html')
diff --git a/src/node/markdown/plugins/link.ts b/src/node/markdown/plugins/link.ts
index 9aa29c96..841cd4cd 100644
--- a/src/node/markdown/plugins/link.ts
+++ b/src/node/markdown/plugins/link.ts
@@ -38,8 +38,8 @@ export const linkPlugin = (
         if (
           // internal anchor links
           !url.startsWith('#') &&
-          // mail links
-          !url.startsWith('mailto:') &&
+          // mail/custom protocol links
+          new URL(url, 'http://a.com').protocol.startsWith('http') &&
           // links to files (other than html/md)
           !/\.(?!html|md)\w+($|\?)/i.test(url)
         ) {