diff --git a/.changeset/gmail-header-case.md b/.changeset/gmail-header-case.md
new file mode 100644
index 000000000..e078d42b2
--- /dev/null
+++ b/.changeset/gmail-header-case.md
@@ -0,0 +1,5 @@
+---
+"@googleworkspace/cli": patch
+---
+
+Match Gmail message header names case-insensitively, so `CC` from Exchange/Outlook senders is no longer dropped by `gmail +reply-all` and `gmail +read`
diff --git a/crates/google-workspace-cli/src/helpers/gmail/mod.rs b/crates/google-workspace-cli/src/helpers/gmail/mod.rs
index caeb8b6b0..c001dd029 100644
--- a/crates/google-workspace-cli/src/helpers/gmail/mod.rs
+++ b/crates/google-workspace-cli/src/helpers/gmail/mod.rs
@@ -258,15 +258,18 @@ fn parse_message_headers(headers: &[Value]) -> ParsedMessageHeaders {
         let name = header.get("name").and_then(|v| v.as_str()).unwrap_or("");
         let value = header.get("value").and_then(|v| v.as_str()).unwrap_or("");
 
-        match name {
-            "From" => parsed.from = value.to_string(),
-            "Reply-To" => append_address_list_header_value(&mut parsed.reply_to, value),
-            "To" => append_address_list_header_value(&mut parsed.to, value),
-            "Cc" => append_address_list_header_value(&mut parsed.cc, value),
-            "Subject" => parsed.subject = value.to_string(),
-            "Date" => parsed.date = value.to_string(),
-            "Message-ID" | "Message-Id" => parsed.message_id = value.to_string(),
-            "References" => append_header_value(&mut parsed.references, value),
+        // Header names are case-insensitive, and the API hands through whatever casing
+        // the sending MTA used. Exchange/Outlook emit "CC"/"MESSAGE-ID", which used to
+        // fall through the match below and get dropped.
+        match name.to_ascii_lowercase().as_str() {
+            "from" => parsed.from = value.to_string(),
+            "reply-to" => append_address_list_header_value(&mut parsed.reply_to, value),
+            "to" => append_address_list_header_value(&mut parsed.to, value),
+            "cc" => append_address_list_header_value(&mut parsed.cc, value),
+            "subject" => parsed.subject = value.to_string(),
+            "date" => parsed.date = value.to_string(),
+            "message-id" => parsed.message_id = value.to_string(),
+            "references" => append_header_value(&mut parsed.references, value),
             _ => {}
         }
     }
@@ -2427,6 +2430,50 @@ mod tests {
         assert_eq!(original.body_html.as_deref(), Some("<p>HTML only</p>"));
     }
 
+    #[test]
+    fn test_parse_original_message_accepts_non_canonical_header_casing() {
+        // Exchange/Outlook style casing: the old case-sensitive match dropped CC and
+        // blew up on the missing From header.
+        let msg = json!({
+            "threadId": "thread-789",
+            "snippet": "",
+            "payload": {
+                "mimeType": "text/plain",
+                "headers": [
+                    { "name": "FROM", "value": "alice@example.com" },
+                    { "name": "TO", "value": "bob@example.com" },
+                    { "name": "cc", "value": "carol@example.com" },
+                    { "name": "CC", "value": "dave@example.com" },
+                    { "name": "Subject", "value": "Hello" },
+                    { "name": "DATE", "value": "Fri, 6 Mar 2026 12:00:00 +0000" },
+                    { "name": "message-id", "value": "<msg@example.com>" },
+                    { "name": "REPLY-TO", "value": "team@example.com" },
+                    { "name": "references", "value": "<ref-1@example.com>" }
+                ],
+                "body": {
+                    "data": URL_SAFE.encode("hi")
+                }
+            }
+        });
+
+        let original = parse_original_message(&msg).unwrap();
+
+        assert_eq!(original.from.email, "alice@example.com");
+        assert_eq!(original.to.len(), 1);
+        assert_eq!(original.to[0].email, "bob@example.com");
+        let cc = original.cc.unwrap();
+        assert_eq!(cc.len(), 2);
+        assert_eq!(cc[0].email, "carol@example.com");
+        assert_eq!(cc[1].email, "dave@example.com");
+        assert_eq!(original.reply_to.unwrap()[0].email, "team@example.com");
+        assert_eq!(original.message_id, "msg@example.com");
+        assert_eq!(original.references, vec!["ref-1@example.com"]);
+        assert_eq!(
+            original.date.as_deref(),
+            Some("Fri, 6 Mar 2026 12:00:00 +0000")
+        );
+    }
+
     #[test]
     fn test_parse_original_message_multipart_alternative() {
         let msg = json!({