diff --git a/src/openforms/formio/api/validators.py b/src/openforms/formio/api/validators.py
index 34dcd5aa13..a6a260ae03 100644
--- a/src/openforms/formio/api/validators.py
+++ b/src/openforms/formio/api/validators.py
@@ -111,6 +111,11 @@ 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