diff --git a/scipost_django/mails/core.py b/scipost_django/mails/core.py
index 7ece3c069f7f3b106cc0f6ba36753dda832c9f18..1225035c54ccf2b016cda962206191fee46ec00a 100644
--- a/scipost_django/mails/core.py
+++ b/scipost_django/mails/core.py
@@ -39,9 +39,9 @@ class MailEngine:
         self,
         mail_code,
         subject="",
-        recipient_list=[],
-        cc=[],
-        bcc=[],
+        recipient_list=None,
+        cc=None,
+        bcc=None,
         from_email="",
         from_name="",
         **kwargs,
@@ -62,6 +62,7 @@ class MailEngine:
         -- from_email (str, optional): Plain email address.
         -- from_name (str, optional): Display name for from address.
         """
+
         self.mail_code = mail_code
         self.extra_config = {
             "cc": cc,
diff --git a/scipost_django/mails/forms.py b/scipost_django/mails/forms.py
index af8ef8f9ecb2018c81d08dd893b3dce6fb247f30..21f77127fd41d7eea73dfc924e14b87441ba39f2 100644
--- a/scipost_django/mails/forms.py
+++ b/scipost_django/mails/forms.py
@@ -28,7 +28,6 @@ class EmailForm(forms.Form):
 
     def __init__(self, *args, **kwargs):
         self.mail_code = kwargs.pop("mail_code")
-
         # Check if all exta configurations are valid.
         self.extra_config.update(kwargs.pop("mail_config", {}))
 
@@ -82,7 +81,10 @@ class EmailForm(forms.Form):
         self.engine.render_template(self.cleaned_data["text"])
         self.engine.mail_data["subject"] = self.cleaned_data["subject"]
         if cc_mail_str := self.cleaned_data["cc_mail_field"]:
-            self.engine.mail_data["cc"] += [m.strip() for m in cc_mail_str.split(",")]
+            if self.engine.mail_data["cc"]:
+                self.engine.mail_data["cc"] += [m.strip() for m in cc_mail_str.split(",")]
+            else:
+                self.engine.mail_data["cc"] = [m.strip() for m in cc_mail_str.split(",")]
         if bcc_mail_str := self.cleaned_data["bcc_mail_field"]:
             self.engine.mail_data["bcc"] += [m.strip() for m in bcc_mail_str.split(",")]
         self.engine.send_mail()