Support SES options via mail message headers

This makes it possible to set new options (like `email_tags`) for each individual email message.

lib/mail/ses/options_builder.rb

@@ -22,7 +22,7 @@ def initialize(message, options = {})
 
       # Returns the options for Aws::SESV2::Client#send_email.
       def build
-        message_options.merge(ses_options)
+        message_options.merge(ses_options, ses_options_from_message)
       end
 
       private
@@ -32,6 +32,17 @@ def ses_options
         slice_hash(@options, *SES_FIELDS)
       end
 
+      def ses_options_from_message
+        mail_options = @message[:mail_options]&.unparsed_value
+
+        if mail_options
+          @message[:mail_options] = nil
+          slice_hash(mail_options, *SES_FIELDS)
+        else
+          {}
+        end
+      end
+
       def message_options
         {
           from_email_address: extract_value(:from)&.first,

spec/options_builder_spec.rb

@@ -102,6 +102,42 @@
       it { expect(subject).to eq(exp) }
     end
 
+    context "with options on the mail object" do
+      let(:mail) do
+        Mail.new do
+          from '"My From" <[email protected]>'
+          reply_to ["[email protected]", "", "My Reply-To <[email protected]>"]
+          to ["[email protected]", "My To <[email protected]>", ""]
+          cc ["", "[email protected]", "My CC <[email protected]>"]
+          bcc ["My BCC <[email protected]>", "", "[email protected]"]
+          body "This is the body"
+          headers(mail_options: {email_tags: [{name: "Foo", value: "Bar"}]})
+        end
+      end
+
+      let(:exp) do
+        {
+          from_email_address: "My From <[email protected]>",
+          reply_to_addresses: ["[email protected]", "My Reply-To <[email protected]>"],
+          destination: {
+            to_addresses: ["[email protected]", "My To <[email protected]>"],
+            cc_addresses: ["[email protected]", "My CC <[email protected]>"],
+            bcc_addresses: ["My BCC <[email protected]>", "[email protected]"]
+          },
+          email_tags: [
+            {name: "Foo", value: "Bar"}
+          ],
+          content: {
+            raw: {
+              data: "Fixed message body"
+            }
+          }
+        }
+      end
+
+      it { expect(subject).to eq(exp) }
+    end
+
     context "when addresses contain non-ascii chars" do
       let(:mail) do
         Mail.new do