diff --git a/app/mailers/conversation_reply_mailer.rb b/app/mailers/conversation_reply_mailer.rb
index 2913fffef..d30c58ab1 100644
--- a/app/mailers/conversation_reply_mailer.rb
+++ b/app/mailers/conversation_reply_mailer.rb
@@ -35,9 +35,8 @@ class ConversationReplyMailer < ApplicationMailer
   end
 
   def email_reply(message)
-    return unless smtp_config_set_or_development?
-
     init_conversation_attributes(message.conversation)
+    return unless smtp_config_set_or_development? || email_oauth_enabled
 
     @message = message
     prepare_mail(true)
diff --git a/app/services/email/send_on_email_service.rb b/app/services/email/send_on_email_service.rb
index 64fe4a381..4786cd56f 100644
--- a/app/services/email/send_on_email_service.rb
+++ b/app/services/email/send_on_email_service.rb
@@ -5,10 +5,15 @@ class Email::SendOnEmailService < Base::SendOnChannelService
     Channel::Email
   end
 
-  def perform_reply
+  def perform_reply # rubocop:disable Metrics/AbcSize
     return unless message.email_notifiable_message?
 
-    reply_mail = ConversationReplyMailer.with(account: message.account).email_reply(message).deliver_now
+    mail = ConversationReplyMailer.with(account: message.account).email_reply(message)
+    raise "Email could not be prepared for message #{message.id}" if mail.nil?
+
+    reply_mail = mail.deliver_now
+    raise "Email delivery returned nil for message #{message.id}" if reply_mail.nil?
+
     Rails.logger.info("Email message #{message.id} sent with source_id: #{reply_mail.message_id}")
     message.update!(source_id: reply_mail.message_id)
   rescue StandardError => e
diff --git a/spec/services/email/send_on_email_service_spec.rb b/spec/services/email/send_on_email_service_spec.rb
index 5a4997eb0..f950862a4 100644
--- a/spec/services/email/send_on_email_service_spec.rb
+++ b/spec/services/email/send_on_email_service_spec.rb
@@ -57,6 +57,39 @@ describe Email::SendOnEmailService do
       end
     end
 
+    context 'when email_reply returns nil' do
+      let(:exception_tracker) { instance_double(ChatwootExceptionTracker, capture_exception: true) }
+
+      before do
+        allow(mailer_context).to receive(:email_reply).with(message).and_return(nil)
+        allow(ChatwootExceptionTracker).to receive(:new).and_return(exception_tracker)
+      end
+
+      it 'marks the message as failed with preparation error' do
+        service.perform
+
+        expect(message.reload.status).to eq('failed')
+        expect(message.reload.external_error).to include("Email could not be prepared for message #{message.id}")
+      end
+    end
+
+    context 'when deliver_now returns nil' do
+      let(:exception_tracker) { instance_double(ChatwootExceptionTracker, capture_exception: true) }
+
+      before do
+        allow(mailer_context).to receive(:email_reply).with(message).and_return(delivery)
+        allow(delivery).to receive(:deliver_now).and_return(nil)
+        allow(ChatwootExceptionTracker).to receive(:new).and_return(exception_tracker)
+      end
+
+      it 'marks the message as failed' do
+        service.perform
+
+        expect(message.reload.status).to eq('failed')
+        expect(message.reload.external_error).to include("Email delivery returned nil for message #{message.id}")
+      end
+    end
+
     context 'when an error occurs' do
       let(:error_message) { 'SMTP connection failed' }
       let(:error) { StandardError.new(error_message) }