add parsing of sender header

Author: yech199

lib/mail/parsers/rfc_2822.ex

@@ -445,6 +445,11 @@ defmodule Mail.Parsers.RFC2822 do
   defp parse_header_value("from", value),
     do: parse_recipient_value(value)
 
+  # If present, the Sender header always contains only one recipient
+  # If not present, the Sender will be nil
+  defp parse_header_value("sender", value),
+    do: parse_recipient_value(value) |> List.first()
+
   defp parse_header_value("reply-to", value),
     do: parse_recipient_value(value)
 
@@ -475,7 +480,7 @@ defmodule Mail.Parsers.RFC2822 do
     do: datetime
 
   defp decode_header_value(key, addresses, opts)
-       when key in ["to", "cc", "bcc", "from", "reply-to"] and is_list(addresses) do
+       when key in ["to", "cc", "bcc", "from", "sender", "reply-to"] and is_list(addresses) do
     addresses =
       Enum.map(addresses, fn
         {name, email} ->
@@ -489,12 +494,12 @@ defmodule Mail.Parsers.RFC2822 do
     addresses
   end
 
-  defp decode_header_value("from", {_name, _address} = value, opts) do
-    [from] = decode_header_value("from", [value], opts)
-    from
+  defp decode_header_value("sender", {_name, _address} = value, opts) do
+    [sender] = decode_header_value("sender", [value], opts)
+    sender
   end
 
-  defp decode_header_value("from", value, _opts), do: value
+  defp decode_header_value("sender", value, _opts), do: value
 
   defp decode_header_value("received", value, _opts),
     do: value

test/mail/parsers/rfc_2822_test.exs

@@ -196,6 +196,27 @@ defmodule Mail.Parsers.RFC2822Test do
     assert Mail.get_html(message) == html_part2
   end
 
+  describe "parses a message with a sender" do
+    # The sender field, if present, can only contain a single recipient
+    test "single sender" do
+      message =
+        parse_email("""
+        Sender: "John Doe" <other@example.com>
+        """)
+
+      assert message.headers["sender"] == {"John Doe", "other@example.com"}
+    end
+
+    test "multiple senders return only the first sender" do
+      message =
+        parse_email("""
+        Sender: user@example.com, "John Doe" <other@example.com>
+        """)
+
+      assert message.headers["sender"] == "user@example.com"
+    end
+  end
+
   describe "parses a message with multiple recipients" do
     test "multiple recipients in To header" do
       # Multiple recipients where some have names can be interpreted as a header value with params if not handled correctly.