diff --git a/package-lock.json b/package-lock.json
index fa6c1ec..4b02250 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -8,6 +8,7 @@
       "name": "papers",
       "version": "0.1.0",
       "dependencies": {
+        "@devmehq/email-validator-js": "^2.10.2",
         "@dnd-kit/core": "^6.3.1",
         "@dnd-kit/sortable": "^10.0.0",
         "@dnd-kit/utilities": "^3.2.2",
@@ -24,10 +25,10 @@
         "@radix-ui/react-switch": "^1.1.4",
         "@remixicon/react": "^4.6.0",
         "@t3-oss/env-nextjs": "^0.10.1",
-        "@types/mongoose": "^5.11.97",
         "@types/node": "^24.6.1",
         "@ungap/with-resolvers": "^0.1.0",
         "@upstash/ratelimit": "^2.0.5",
+        "@upstash/redis": "^1.33.0",
         "@vercel/kv": "^3.0.0",
         "axios": "^1.8.4",
         "canvas": "^3.2.0",
@@ -99,6 +100,20 @@
         "node": ">=6.9.0"
       }
     },
+    "node_modules/@devmehq/email-validator-js": {
+      "version": "2.10.4",
+      "resolved": "https://registry.npmjs.org/@devmehq/email-validator-js/-/email-validator-js-2.10.4.tgz",
+      "integrity": "sha512-yZ83B2PaQT1lwdKLQJTTxT91fC7EGtZODFVTq1ZQoeA7h1yxq0RFg29w+jNUAx7slPTpQgjdeW+sI3/oIkA+uQ==",
+      "license": "BSL 1.1",
+      "dependencies": {
+        "psl": "^1.15.0",
+        "string-similarity-js": "^2.1.4",
+        "tiny-lru": "^11.4.5"
+      },
+      "engines": {
+        "node": ">= 12.0"
+      }
+    },
     "node_modules/@dnd-kit/accessibility": {
       "version": "3.1.1",
       "resolved": "https://registry.npmjs.org/@dnd-kit/accessibility/-/accessibility-3.1.1.tgz",
@@ -734,6 +749,66 @@
         "glob": "10.3.10"
       }
     },
+    "node_modules/@next/swc-darwin-arm64": {
+      "version": "14.2.32",
+      "resolved": "https://registry.npmjs.org/@next/swc-darwin-arm64/-/swc-darwin-arm64-14.2.32.tgz",
+      "integrity": "sha512-osHXveM70zC+ilfuFa/2W6a1XQxJTvEhzEycnjUaVE8kpUS09lDpiDDX2YLdyFCzoUbvbo5r0X1Kp4MllIOShw==",
+      "cpu": [
+        "arm64"
+      ],
+      "optional": true,
+      "os": [
+        "darwin"
+      ],
+      "engines": {
+        "node": ">= 10"
+      }
+    },
+    "node_modules/@next/swc-darwin-x64": {
+      "version": "14.2.32",
+      "resolved": "https://registry.npmjs.org/@next/swc-darwin-x64/-/swc-darwin-x64-14.2.32.tgz",
+      "integrity": "sha512-P9NpCAJuOiaHHpqtrCNncjqtSBi1f6QUdHK/+dNabBIXB2RUFWL19TY1Hkhu74OvyNQEYEzzMJCMQk5agjw1Qg==",
+      "cpu": [
+        "x64"
+      ],
+      "optional": true,
+      "os": [
+        "darwin"
+      ],
+      "engines": {
+        "node": ">= 10"
+      }
+    },
+    "node_modules/@next/swc-linux-arm64-gnu": {
+      "version": "14.2.32",
+      "resolved": "https://registry.npmjs.org/@next/swc-linux-arm64-gnu/-/swc-linux-arm64-gnu-14.2.32.tgz",
+      "integrity": "sha512-v7JaO0oXXt6d+cFjrrKqYnR2ubrD+JYP7nQVRZgeo5uNE5hkCpWnHmXm9vy3g6foMO8SPwL0P3MPw1c+BjbAzA==",
+      "cpu": [
+        "arm64"
+      ],
+      "optional": true,
+      "os": [
+        "linux"
+      ],
+      "engines": {
+        "node": ">= 10"
+      }
+    },
+    "node_modules/@next/swc-linux-arm64-musl": {
+      "version": "14.2.32",
+      "resolved": "https://registry.npmjs.org/@next/swc-linux-arm64-musl/-/swc-linux-arm64-musl-14.2.32.tgz",
+      "integrity": "sha512-tA6sIKShXtSJBTH88i0DRd6I9n3ZTirmwpwAqH5zdJoQF7/wlJXR8DkPmKwYl5mFWhEKr5IIa3LfpMW9RRwKmQ==",
+      "cpu": [
+        "arm64"
+      ],
+      "optional": true,
+      "os": [
+        "linux"
+      ],
+      "engines": {
+        "node": ">= 10"
+      }
+    },
     "node_modules/@next/swc-linux-x64-gnu": {
       "version": "14.2.32",
       "resolved": "https://registry.npmjs.org/@next/swc-linux-x64-gnu/-/swc-linux-x64-gnu-14.2.32.tgz",
@@ -766,6 +841,51 @@
         "node": ">= 10"
       }
     },
+    "node_modules/@next/swc-win32-arm64-msvc": {
+      "version": "14.2.32",
+      "resolved": "https://registry.npmjs.org/@next/swc-win32-arm64-msvc/-/swc-win32-arm64-msvc-14.2.32.tgz",
+      "integrity": "sha512-rORQjXsAFeX6TLYJrCG5yoIDj+NKq31Rqwn8Wpn/bkPNy5rTHvOXkW8mLFonItS7QC6M+1JIIcLe+vOCTOYpvg==",
+      "cpu": [
+        "arm64"
+      ],
+      "optional": true,
+      "os": [
+        "win32"
+      ],
+      "engines": {
+        "node": ">= 10"
+      }
+    },
+    "node_modules/@next/swc-win32-ia32-msvc": {
+      "version": "14.2.32",
+      "resolved": "https://registry.npmjs.org/@next/swc-win32-ia32-msvc/-/swc-win32-ia32-msvc-14.2.32.tgz",
+      "integrity": "sha512-jHUeDPVHrgFltqoAqDB6g6OStNnFxnc7Aks3p0KE0FbwAvRg6qWKYF5mSTdCTxA3axoSAUwxYdILzXJfUwlHhA==",
+      "cpu": [
+        "ia32"
+      ],
+      "optional": true,
+      "os": [
+        "win32"
+      ],
+      "engines": {
+        "node": ">= 10"
+      }
+    },
+    "node_modules/@next/swc-win32-x64-msvc": {
+      "version": "14.2.32",
+      "resolved": "https://registry.npmjs.org/@next/swc-win32-x64-msvc/-/swc-win32-x64-msvc-14.2.32.tgz",
+      "integrity": "sha512-2N0lSoU4GjfLSO50wvKpMQgKd4HdI2UHEhQPPPnlgfBJlOgJxkjpkYBqzk08f1gItBB6xF/n+ykso2hgxuydsA==",
+      "cpu": [
+        "x64"
+      ],
+      "optional": true,
+      "os": [
+        "win32"
+      ],
+      "engines": {
+        "node": ">= 10"
+      }
+    },
     "node_modules/@nodelib/fs.scandir": {
       "version": "2.1.5",
       "resolved": "https://registry.npmjs.org/@nodelib/fs.scandir/-/fs.scandir-2.1.5.tgz",
@@ -1793,16 +1913,6 @@
       "dev": true,
       "license": "MIT"
     },
-    "node_modules/@types/mongoose": {
-      "version": "5.11.97",
-      "resolved": "https://registry.npmjs.org/@types/mongoose/-/mongoose-5.11.97.tgz",
-      "integrity": "sha512-cqwOVYT3qXyLiGw7ueU2kX9noE8DPGRY6z8eUxudhXY8NZ7DMKYAxyZkLSevGfhCX3dO/AoX5/SO9lAzfjon0Q==",
-      "deprecated": "Mongoose publishes its own types, so you do not need to install this package.",
-      "license": "MIT",
-      "dependencies": {
-        "mongoose": "*"
-      }
-    },
     "node_modules/@types/node": {
       "version": "24.6.2",
       "resolved": "https://registry.npmjs.org/@types/node/-/node-24.6.2.tgz",
@@ -7956,6 +8066,18 @@
       "integrity": "sha512-D+zkORCbA9f1tdWRK0RaCR3GPv50cMxcrz4X8k5LTSUD1Dkw47mKJEZQNunItRTkWwgtaUSo1RVFRIG9ZXiFYg==",
       "license": "MIT"
     },
+    "node_modules/psl": {
+      "version": "1.15.0",
+      "resolved": "https://registry.npmjs.org/psl/-/psl-1.15.0.tgz",
+      "integrity": "sha512-JZd3gMVBAVQkSs6HdNZo9Sdo0LNcQeMNP3CozBJb3JYC/QUYZTnKxP+f8oWRX4rHP5EurWxqAHTSwUCjlNKa1w==",
+      "license": "MIT",
+      "dependencies": {
+        "punycode": "^2.3.1"
+      },
+      "funding": {
+        "url": "https://github.com/sponsors/lupomontero"
+      }
+    },
     "node_modules/pump": {
       "version": "3.0.3",
       "resolved": "https://registry.npmjs.org/pump/-/pump-3.0.3.tgz",
@@ -9042,6 +9164,12 @@
       "integrity": "sha512-Gd2UZBJDkXlY7GbJxfsE8/nvKkUEU1G38c1siN6QP6a9PT9MmHB8GnpscSmMJSoF8LOIrt8ud/wPtojys4G6+g==",
       "license": "MIT"
     },
+    "node_modules/string-similarity-js": {
+      "version": "2.1.4",
+      "resolved": "https://registry.npmjs.org/string-similarity-js/-/string-similarity-js-2.1.4.tgz",
+      "integrity": "sha512-uApODZNjCHGYROzDSAdCmAHf60L/pMDHnP/yk6TAbvGg7JSPZlSto/ceCI7hZEqzc53/juU2aOJFkM2yUVTMTA==",
+      "license": "MIT"
+    },
     "node_modules/string-width": {
       "version": "5.1.2",
       "resolved": "https://registry.npmjs.org/string-width/-/string-width-5.1.2.tgz",
@@ -9744,6 +9872,15 @@
       "integrity": "sha512-+FbBPE1o9QAYvviau/qC5SE3caw21q3xkvWKBtja5vgqOWIHHJ3ioaq1VPfn/Szqctz2bU/oYeKd9/z5BL+PVg==",
       "license": "MIT"
     },
+    "node_modules/tiny-lru": {
+      "version": "11.4.5",
+      "resolved": "https://registry.npmjs.org/tiny-lru/-/tiny-lru-11.4.5.tgz",
+      "integrity": "sha512-hkcz3FjNJfKXjV4mjQ1OrXSLAehg8Hw+cEZclOVT+5c/cWQWImQ9wolzTjth+dmmDe++p3bme3fTxz6Q4Etsqw==",
+      "license": "BSD-3-Clause",
+      "engines": {
+        "node": ">=12"
+      }
+    },
     "node_modules/tinyglobby": {
       "version": "0.2.14",
       "resolved": "https://registry.npmjs.org/tinyglobby/-/tinyglobby-0.2.14.tgz",
@@ -10755,111 +10892,6 @@
       "funding": {
         "url": "https://github.com/sponsors/colinhacks"
       }
-    },
-    "node_modules/@next/swc-darwin-arm64": {
-      "version": "14.2.32",
-      "resolved": "https://registry.npmjs.org/@next/swc-darwin-arm64/-/swc-darwin-arm64-14.2.32.tgz",
-      "integrity": "sha512-osHXveM70zC+ilfuFa/2W6a1XQxJTvEhzEycnjUaVE8kpUS09lDpiDDX2YLdyFCzoUbvbo5r0X1Kp4MllIOShw==",
-      "cpu": [
-        "arm64"
-      ],
-      "optional": true,
-      "os": [
-        "darwin"
-      ],
-      "engines": {
-        "node": ">= 10"
-      }
-    },
-    "node_modules/@next/swc-darwin-x64": {
-      "version": "14.2.32",
-      "resolved": "https://registry.npmjs.org/@next/swc-darwin-x64/-/swc-darwin-x64-14.2.32.tgz",
-      "integrity": "sha512-P9NpCAJuOiaHHpqtrCNncjqtSBi1f6QUdHK/+dNabBIXB2RUFWL19TY1Hkhu74OvyNQEYEzzMJCMQk5agjw1Qg==",
-      "cpu": [
-        "x64"
-      ],
-      "optional": true,
-      "os": [
-        "darwin"
-      ],
-      "engines": {
-        "node": ">= 10"
-      }
-    },
-    "node_modules/@next/swc-linux-arm64-gnu": {
-      "version": "14.2.32",
-      "resolved": "https://registry.npmjs.org/@next/swc-linux-arm64-gnu/-/swc-linux-arm64-gnu-14.2.32.tgz",
-      "integrity": "sha512-v7JaO0oXXt6d+cFjrrKqYnR2ubrD+JYP7nQVRZgeo5uNE5hkCpWnHmXm9vy3g6foMO8SPwL0P3MPw1c+BjbAzA==",
-      "cpu": [
-        "arm64"
-      ],
-      "optional": true,
-      "os": [
-        "linux"
-      ],
-      "engines": {
-        "node": ">= 10"
-      }
-    },
-    "node_modules/@next/swc-linux-arm64-musl": {
-      "version": "14.2.32",
-      "resolved": "https://registry.npmjs.org/@next/swc-linux-arm64-musl/-/swc-linux-arm64-musl-14.2.32.tgz",
-      "integrity": "sha512-tA6sIKShXtSJBTH88i0DRd6I9n3ZTirmwpwAqH5zdJoQF7/wlJXR8DkPmKwYl5mFWhEKr5IIa3LfpMW9RRwKmQ==",
-      "cpu": [
-        "arm64"
-      ],
-      "optional": true,
-      "os": [
-        "linux"
-      ],
-      "engines": {
-        "node": ">= 10"
-      }
-    },
-    "node_modules/@next/swc-win32-arm64-msvc": {
-      "version": "14.2.32",
-      "resolved": "https://registry.npmjs.org/@next/swc-win32-arm64-msvc/-/swc-win32-arm64-msvc-14.2.32.tgz",
-      "integrity": "sha512-rORQjXsAFeX6TLYJrCG5yoIDj+NKq31Rqwn8Wpn/bkPNy5rTHvOXkW8mLFonItS7QC6M+1JIIcLe+vOCTOYpvg==",
-      "cpu": [
-        "arm64"
-      ],
-      "optional": true,
-      "os": [
-        "win32"
-      ],
-      "engines": {
-        "node": ">= 10"
-      }
-    },
-    "node_modules/@next/swc-win32-ia32-msvc": {
-      "version": "14.2.32",
-      "resolved": "https://registry.npmjs.org/@next/swc-win32-ia32-msvc/-/swc-win32-ia32-msvc-14.2.32.tgz",
-      "integrity": "sha512-jHUeDPVHrgFltqoAqDB6g6OStNnFxnc7Aks3p0KE0FbwAvRg6qWKYF5mSTdCTxA3axoSAUwxYdILzXJfUwlHhA==",
-      "cpu": [
-        "ia32"
-      ],
-      "optional": true,
-      "os": [
-        "win32"
-      ],
-      "engines": {
-        "node": ">= 10"
-      }
-    },
-    "node_modules/@next/swc-win32-x64-msvc": {
-      "version": "14.2.32",
-      "resolved": "https://registry.npmjs.org/@next/swc-win32-x64-msvc/-/swc-win32-x64-msvc-14.2.32.tgz",
-      "integrity": "sha512-2N0lSoU4GjfLSO50wvKpMQgKd4HdI2UHEhQPPPnlgfBJlOgJxkjpkYBqzk08f1gItBB6xF/n+ykso2hgxuydsA==",
-      "cpu": [
-        "x64"
-      ],
-      "optional": true,
-      "os": [
-        "win32"
-      ],
-      "engines": {
-        "node": ">= 10"
-      }
     }
   }
 }
diff --git a/src/app/upload/page.tsx b/src/app/upload/page.tsx
index 18533bb..4c3c26d 100644
--- a/src/app/upload/page.tsx
+++ b/src/app/upload/page.tsx
@@ -114,7 +114,7 @@ export default function Page() {
       }
 
       if (isNewPdf && hasExistingPdf) {
-        toast.error("Only one PDF is allowed. You’ve already uploaded a PDF.", {
+        toast.error("Only one PDF is allowed. You've already uploaded a PDF.", {
           id: toastId,
         });
         return;
@@ -136,11 +136,8 @@ export default function Page() {
         return;
       }
 
-      const totalSize = allFiles.reduce(
-        (sum, f) => sum + f.size,
-        0,
-      );
-      if (totalSize > maxFileSize){
+      const totalSize = allFiles.reduce((sum, f) => sum + f.size, 0);
+      if (totalSize > maxFileSize) {
         toast.error("The total upload size exceeds 5MB.", { id: toastId });
         return;
       }
@@ -440,8 +437,8 @@ export default function Page() {
                       strategy={horizontalListSortingStrategy}
                     >
                       <div className="flex w-full snap-x snap-mandatory gap-3 sm:gap-4 md:gap-5">
-                        {previews.map((item, index) => (
-                          <SortablePreview key={item.id} id={item.id}>
+                        {previews.map((item, index) => {
+                          const previewContent = (
                             <div className="group relative w-full flex-shrink-0 snap-start sm:w-1/2 md:w-1/3 lg:w-1/4">
                               <div className="relative h-64 w-48 overflow-hidden rounded-xl outline outline-2 outline-white sm:h-60">
                                 {/* Index badge */}
@@ -486,8 +483,17 @@ export default function Page() {
                                 </div>
                               </div>
                             </div>
-                          </SortablePreview>
-                        ))}
+                          );
+
+                          // Only wrap in SortablePreview if there are multiple files
+                          return previews.length > 1 ? (
+                            <SortablePreview key={item.id} id={item.id}>
+                              {previewContent}
+                            </SortablePreview>
+                          ) : (
+                            <div key={item.id}>{previewContent}</div>
+                          );
+                        })}
                       </div>
 
                       {previews.length > 2 && (