diff --git a/src/openforms/formio/api/validators.py b/src/openforms/formio/api/validators.py
index 34dcd5aa13..b1821a1463 100644
--- a/src/openforms/formio/api/validators.py
+++ b/src/openforms/formio/api/validators.py
@@ -56,7 +56,8 @@ def __init__(self, allowed_mime_types: Iterable[str] | None = None):
 
     def __call__(self, value: UploadedFile) -> None:
         head = value.read(2048)
-        ext = value.name.split(".")[-1]
+        file_name_parts = value.name.split(".")
+        ext = file_name_parts[-1]
         mime_type = magic.from_buffer(head, mime=True)
 
         # gh #2520
@@ -76,6 +77,12 @@ def __call__(self, value: UploadedFile) -> None:
                 _("The provided file is not a valid file type.")
             )
 
+        if len(file_name_parts) == 1:
+            raise serializers.ValidationError(
+                _("Could not determine the file type. Please make sure the file name "
+                "has an extension.")
+            )
+
         # Contents is allowed. Do extension or submitted content_type agree?
         if value.content_type == "application/octet-stream":
             m = magic.Magic(extension=True)
@@ -111,6 +118,11 @@ def __call__(self, value: UploadedFile) -> None:
             "image/heif",
         ):
             return
+        # 4795
+        # The sdk cannot determine the file type of .msg files, which result into
+        # content_type "". So we have to validate these for ourselves
+        elif mime_type == "application/vnd.ms-outlook" and ext == "msg":
+            return
 
         # gh #4658
         # Windows use application/x-zip-compressed as a mimetype for .zip files, which
diff --git a/src/openforms/formio/components/vanilla.py b/src/openforms/formio/components/vanilla.py
index 109cb0560d..d5e6a7937a 100644
--- a/src/openforms/formio/components/vanilla.py
+++ b/src/openforms/formio/components/vanilla.py
@@ -338,14 +338,7 @@ class FileSerializer(serializers.Serializer):
     originalName = serializers.CharField(trim_whitespace=False)
     size = serializers.IntegerField(min_value=0)
     storage = serializers.ChoiceField(choices=["url"])
-    type = serializers.CharField(
-        error_messages={
-            "blank": _(
-                "Could not determine the file type. Please make sure the file name "
-                "has an extension."
-            ),
-        }
-    )
+    type = serializers.CharField(required=False, allow_blank=True)
     url = serializers.URLField()
     data = FileDataSerializer()  # type: ignore