diff --git a/src/happening/utils.py b/src/happening/utils.py
index d682a58..7963499 100644
--- a/src/happening/utils.py
+++ b/src/happening/utils.py
@@ -158,7 +158,7 @@ def externalise_urls(text):
 def externalise_url(url):
     """Convert a single URL from internal to external."""
     from pages.configuration import ForceSSL
-    if url.startswith("http"):
+    if url.startswith("http:") or url.startswith("mailto:"):
         # Already absolute
         return url