diff --git a/mail_panel/backend.py b/mail_panel/backend.py
index e9dbde4..901b4b2 100644
--- a/mail_panel/backend.py
+++ b/mail_panel/backend.py
@@ -8,11 +8,14 @@
 
 
 class MailToolbarBackendEmail(mail.EmailMultiAlternatives):
-    def __init__(self, message):
-        try:
-            self.id = uuid4().get_hex()
-        except AttributeError:
-            self.id = uuid4().hex  # python 3
+    def __init__(self, message, id=None):
+        if id:
+            self.id = id
+        else:
+            try:
+                self.id = uuid4().get_hex()
+            except AttributeError:
+                self.id = uuid4().hex  # python 3
         self.date_sent = now()
         self.read = False
         message.message()  # triggers header validation
diff --git a/mail_panel/utils.py b/mail_panel/utils.py
index d944a9c..259e957 100644
--- a/mail_panel/utils.py
+++ b/mail_panel/utils.py
@@ -1,4 +1,5 @@
 from django.core.cache import caches
+from django.core.mail import EmailMultiAlternatives
 
 try:
     CACHE_SETTINGS = caches.settings
@@ -20,18 +21,67 @@
     cache = caches.create_connection("mail_panel")
 
 
+def serialize_email(email):
+    """
+    Serialize email to a dictionary (prior to caching).
+    """
+    return {
+        "subject": email.subject,
+        "body": email.body,
+        "from_email": email.from_email,
+        "to": email.to,
+        "cc": email.cc,
+        "bcc": email.bcc,
+        "headers": email.extra_headers,
+        "alternatives": email.alternatives,
+    }
+
+
+def deserialize_email(message_id, data):
+    """
+    Deserialize a dictionary representing an email (after getting it from the cache).
+    """
+    from .backend import MailToolbarBackendEmail
+
+    django_email = EmailMultiAlternatives(
+        subject=data["subject"],
+        body=data["body"],
+        from_email=data["from_email"],
+        to=data["to"],
+        cc=data.get("cc", []),
+        bcc=data.get("bcc", []),
+        headers=data.get("headers", {}),
+    )
+    email = MailToolbarBackendEmail(django_email, id=message_id)
+    for alt in data.get("alternatives", []):
+        email.attach_alternative(alt[0], alt[1])
+    return email
+
+
 def load_outbox():
     """
     Returns a dictionary of cached mail.
     """
-    return cache.get(MAIL_TOOLBAR_CACHE_KEY, {})
+    # Since the emails in the cache are serialized, we first deserialize them.
+    outbox_obj_of_serialized_emails = cache.get(MAIL_TOOLBAR_CACHE_KEY, {})
+    outbox = {}
+    for email_id, serialized_email in outbox_obj_of_serialized_emails.items():
+        email = deserialize_email(email_id, serialized_email)
+        outbox[email_id] = email
+    return outbox
 
 
 def save_outbox(outbox):
     """
     Saves the dictionary of cached mail and sets expiry.
     """
-    cache.set(MAIL_TOOLBAR_CACHE_KEY, outbox, MAIL_TOOLBAR_TTL)
+    outbox_obj = {}
+    # Since some emails contain data types that can not be serialized, we first
+    # serialize emails to a serializable object.
+    for email_id, email in outbox.items():
+        outbox_obj[email_id] = serialize_email(email)
+
+    cache.set(MAIL_TOOLBAR_CACHE_KEY, outbox_obj, MAIL_TOOLBAR_TTL)
 
 
 def clear_outbox():