FIX: Replace use of regular expression (#12838)

It used a regular expression to check if message IDs were in RFC format.

spec/components/email/email_spec.rb

@@ -65,4 +65,29 @@ describe Email do
 
   end
 
+  describe "message_id_rfc_format" do
+
+    it "returns message ID in RFC format" do
+      expect(Email.message_id_rfc_format("test@test")).to eq("<test@test>")
+    end
+
+    it "returns input if already in RFC format" do
+      expect(Email.message_id_rfc_format("<test@test>")).to eq("<test@test>")
+    end
+
+  end
+
+  describe "message_id_clean" do
+
+    it "returns message ID if in RFC format" do
+      expect(Email.message_id_clean("<test@test>")).to eq("test@test")
+    end
+
+    it "returns input if a clean message ID is not in RFC format" do
+      message_id = "<" + "@" * 50
+      expect(Email.message_id_clean(message_id)).to eq(message_id)
+    end
+
+  end
+
 end