diff --git a/src/server.js b/src/server.js
index d6c0dcd..27d5514 100644
--- a/src/server.js
+++ b/src/server.js
@@ -46,13 +46,24 @@ app.post('/bot/messenger-login', async (req, res) => {
   }
 
   const userId = String(req.body?.userId || '').trim();
+  const email = String(req.body?.email || '').trim().toLowerCase();
   const channelId = String(req.body?.channelId || '').trim();
-  if (!userId || !channelId) {
-    res.status(400).json({ error: 'userId and channelId are required.' });
+  if (!channelId || (!userId && !email)) {
+    res.status(400).json({ error: 'channelId and (userId or email) are required.' });
     return;
   }
 
-  const user = await prisma.user.findUnique({ where: { id: userId } });
+  const user = userId
+    ? await prisma.user.findUnique({ where: { id: userId } })
+    : await prisma.user.findFirst({
+        where: {
+          email: {
+            equals: email,
+            mode: 'insensitive',
+          },
+        },
+      });
+
   if (!user) {
     res.status(404).json({ error: 'User not found.' });
     return;