diff --git a/app/mailers/merge_completion_mailer.rb b/app/mailers/merge_completion_mailer.rb
index f2a9f8030..a5de27d72 100644
--- a/app/mailers/merge_completion_mailer.rb
+++ b/app/mailers/merge_completion_mailer.rb
@@ -1,10 +1,24 @@
 class MergeCompletionMailer < NotifyMailer
-  MERGE_COMPLETION_TEMPLATE_ID = "b3b62e72-5ced-4515-8720-08bdc7bac792".freeze
+  MERGE_COMPLETION_MERGING_ORGANISATION_TEMPLATE_ID = "b3b62e72-5ced-4515-8720-08bdc7bac792".freeze
+  MERGE_COMPLETION_ABSORBING_ORGANISATION_TEMPLATE_ID = "xxx".freeze
 
-  def send_merge_completion_mail(email, merged_organisation_name, absorbing_organisation_name, merge_date)
+  def send_merged_organisation_success_mail(email, merged_organisation_name, absorbing_organisation_name, merge_date)
     send_email(
       email,
-      MERGE_COMPLETION_TEMPLATE_ID,
+      MERGE_COMPLETION_MERGING_ORGANISATION_TEMPLATE_ID,
+      {
+        merged_organisation_name:,
+        absorbing_organisation_name:,
+        merge_date: merge_date.to_formatted_s(:govuk_date),
+        email:,
+      },
+    )
+  end
+
+  def send_absorbing_organisation_success_mail(email, merged_organisation_name, absorbing_organisation_name, merge_date)
+    send_email(
+      email,
+      MERGE_COMPLETION_ABSORBING_ORGANISATION_TEMPLATE_ID,
       {
         merged_organisation_name:,
         absorbing_organisation_name:,
diff --git a/app/services/merge/merge_organisations_service.rb b/app/services/merge/merge_organisations_service.rb
index ead816dd2..7bca9f6f0 100644
--- a/app/services/merge/merge_organisations_service.rb
+++ b/app/services/merge/merge_organisations_service.rb
@@ -153,9 +153,12 @@ private
   end
 
   def send_success_emails
-    @merged_users.each do |organisation_name, users|
-      users.each do |user|
-        MergeCompletionMailer.send_merge_completion_mail(user[:email], organisation_name, @absorbing_organisation.name, @merge_date).deliver_later
+    @absorbing_organisation.users.each do |user|
+      merged_organisation, merged_user = find_merged_user_and_organization_by_email(user.email)
+      if merged_user.present?
+        MergeCompletionMailer.send_merged_organisation_success_mail(merged_user[:email], merged_organisation, @absorbing_organisation.name, @merge_date).deliver_later
+      else
+        MergeCompletionMailer.send_absorbing_organisation_success_mail(user.email, @merging_organisations.map(&:name).join(", "), @absorbing_organisation.name, @merge_date).deliver_later
       end
     end
   end
@@ -234,4 +237,12 @@ private
       deactivation_period.destroy!
     end
   end
+
+  def find_merged_user_and_organization_by_email(provided_email)
+    @merged_users.each do |org, users|
+      user = users.find { |u| u[:email] == provided_email }
+      return org, user if user
+    end
+    nil
+  end
 end
diff --git a/spec/mailers/merge_completion_mailer_spec.rb b/spec/mailers/merge_completion_mailer_spec.rb
index 0ebe96fcd..fb3f81ebb 100644
--- a/spec/mailers/merge_completion_mailer_spec.rb
+++ b/spec/mailers/merge_completion_mailer_spec.rb
@@ -8,18 +8,39 @@ RSpec.describe MergeCompletionMailer do
     allow(notify_client).to receive(:send_email).and_return(true)
   end
 
-  describe "#send_merge_completion_mail" do
+  describe "#send_merged_organisation_success_mail" do
     let(:merge_date) { Time.zone.local(2023, 1, 1) }
 
     it "sends a merge completion E-mail via notify" do
-      expect(notify_client).to receive(:send_email).with(hash_including({ personalisation: hash_including({
-        merged_organisation_name: "merged organisation",
-        absorbing_organisation_name: "absorbing organisation",
-        merge_date: "1 January 2023",
-        email: "user@example.com",
-      }) }))
-
-      described_class.new.send_merge_completion_mail("user@example.com", "merged organisation", "absorbing organisation", merge_date)
+      expect(notify_client).to receive(:send_email).with(hash_including({
+        template_id: MergeCompletionMailer::MERGE_COMPLETION_MERGING_ORGANISATION_TEMPLATE_ID,
+        personalisation: hash_including({
+          merged_organisation_name: "merged organisation",
+          absorbing_organisation_name: "absorbing organisation",
+          merge_date: "1 January 2023",
+          email: "user@example.com",
+        }),
+      }))
+
+      described_class.new.send_merged_organisation_success_mail("user@example.com", "merged organisation", "absorbing organisation", merge_date)
+    end
+  end
+
+  describe "#send_absorbing_organisation_success_mail" do
+    let(:merge_date) { Time.zone.local(2023, 1, 1) }
+
+    it "sends a merge completion E-mail via notify" do
+      expect(notify_client).to receive(:send_email).with(hash_including({
+        template_id: MergeCompletionMailer::MERGE_COMPLETION_ABSORBING_ORGANISATION_TEMPLATE_ID,
+        personalisation: hash_including({
+          merged_organisation_name: "merged organisation",
+          absorbing_organisation_name: "absorbing organisation",
+          merge_date: "1 January 2023",
+          email: "user@example.com",
+        }),
+      }))
+
+      described_class.new.send_absorbing_organisation_success_mail("user@example.com", "merged organisation", "absorbing organisation", merge_date)
     end
   end
 end
diff --git a/spec/services/merge/merge_organisations_service_spec.rb b/spec/services/merge/merge_organisations_service_spec.rb
index fe6843981..aa813b5dc 100644
--- a/spec/services/merge/merge_organisations_service_spec.rb
+++ b/spec/services/merge/merge_organisations_service_spec.rb
@@ -4,7 +4,8 @@ RSpec.describe Merge::MergeOrganisationsService do
   describe "#call" do
     before do
       mail_double = instance_double("ActionMailer::MessageDelivery", deliver_later: nil)
-      allow(MergeCompletionMailer).to receive(:send_merge_completion_mail).and_return(mail_double)
+      allow(MergeCompletionMailer).to receive(:send_merged_organisation_success_mail).and_return(mail_double)
+      allow(MergeCompletionMailer).to receive(:send_absorbing_organisation_success_mail).and_return(mail_double)
     end
 
     context "when merging a single organisation into an existing organisation" do
@@ -838,8 +839,21 @@ RSpec.describe Merge::MergeOrganisationsService do
       end
 
       it "sends a merge completion E-mail to the merged organisation users" do
-        expect(MergeCompletionMailer).to receive(:send_merge_completion_mail).with(merging_organisation_user.email, "fake org", "absorbing org", Time.zone.today).once
-        expect(MergeCompletionMailer).to receive(:send_merge_completion_mail).with(merging_organisation.data_protection_officers.first.email, "fake org", "absorbing org", Time.zone.today).once
+        expect(MergeCompletionMailer).to receive(:send_merged_organisation_success_mail).with(merging_organisation_user.email, "fake org", "absorbing org", Time.zone.today).once
+        expect(MergeCompletionMailer).to receive(:send_merged_organisation_success_mail).with(merging_organisation.data_protection_officers.first.email, "fake org", "absorbing org", Time.zone.today).once
+
+        expect(MergeCompletionMailer).not_to receive(:send_merged_organisation_success_mail).with(absorbing_organisation.data_protection_officers.first.email, "fake org", "absorbing org", Time.zone.today)
+        expect(MergeCompletionMailer).not_to receive(:send_merged_organisation_success_mail).with(absorbing_organisation_user.email, "fake org", "absorbing org", Time.zone.today)
+
+        merge_organisations_service.call
+      end
+
+      it "sends a merge completion E-mail to the original absorbing organisation users" do
+        expect(MergeCompletionMailer).to receive(:send_absorbing_organisation_success_mail).with(absorbing_organisation.data_protection_officers.first.email, "fake org", "absorbing org", Time.zone.today).once
+        expect(MergeCompletionMailer).to receive(:send_absorbing_organisation_success_mail).with(absorbing_organisation_user.email, "fake org", "absorbing org", Time.zone.today).once
+
+        expect(MergeCompletionMailer).not_to receive(:send_absorbing_organisation_success_mail).with(merging_organisation_user.email, "fake org", "absorbing org", Time.zone.today)
+        expect(MergeCompletionMailer).not_to receive(:send_absorbing_organisation_success_mail).with(merging_organisation.data_protection_officers.first.email, "fake org", "absorbing org", Time.zone.today)
 
         merge_organisations_service.call
       end
@@ -848,7 +862,7 @@ RSpec.describe Merge::MergeOrganisationsService do
     context "when merging a multiple organisations into an existing organisation" do
       subject(:merge_organisations_service) { described_class.new(absorbing_organisation_id: absorbing_organisation.id, merging_organisation_ids: [merging_organisation_ids], merge_date: nil) }
 
-      let(:absorbing_organisation) { create(:organisation, holds_own_stock: false) }
+      let(:absorbing_organisation) { create(:organisation, holds_own_stock: false, name: "absorbing org") }
       let(:absorbing_organisation_user) { create(:user, organisation: absorbing_organisation) }
 
       let(:merging_organisation) { create(:organisation, holds_own_stock: true, name: "fake org") }
@@ -946,6 +960,34 @@ RSpec.describe Merge::MergeOrganisationsService do
           expect(merging_organisation.users.first).to eq(dpo)
           expect(merging_organisation.data_protection_confirmation.data_protection_officer).to eq(dpo)
         end
+
+        it "sends a merge completion E-mail to the merged organisation users" do
+          expect(MergeCompletionMailer).to receive(:send_merged_organisation_success_mail).with(merging_organisation_user.email, "fake org", "absorbing org", Time.zone.today).once
+          expect(MergeCompletionMailer).to receive(:send_merged_organisation_success_mail).with(merging_organisation.data_protection_officers.first.email, "fake org", "absorbing org", Time.zone.today).once
+
+          expect(MergeCompletionMailer).not_to receive(:send_merged_organisation_success_mail).with(absorbing_organisation.data_protection_officers.first.email, "fake org", "absorbing org", Time.zone.today)
+          expect(MergeCompletionMailer).not_to receive(:send_merged_organisation_success_mail).with(absorbing_organisation_user.email, "fake org", "absorbing org", Time.zone.today)
+
+          merging_organisation_too.users.each do |user|
+            expect(MergeCompletionMailer).to receive(:send_merged_organisation_success_mail).with(user.email, "second org", "absorbing org", Time.zone.today).once
+          end
+
+          merge_organisations_service.call
+        end
+
+        it "sends a merge completion E-mail to the original absorbing organisation users" do
+          expect(MergeCompletionMailer).to receive(:send_absorbing_organisation_success_mail).with(absorbing_organisation.data_protection_officers.first.email, "fake org, second org", "absorbing org", Time.zone.today).once
+          expect(MergeCompletionMailer).to receive(:send_absorbing_organisation_success_mail).with(absorbing_organisation_user.email, "fake org, second org", "absorbing org", Time.zone.today).once
+
+          expect(MergeCompletionMailer).not_to receive(:send_absorbing_organisation_success_mail).with(merging_organisation_user.email, "fake org, second org", "absorbing org", Time.zone.today)
+          expect(MergeCompletionMailer).not_to receive(:send_absorbing_organisation_success_mail).with(merging_organisation.data_protection_officers.first.email, "fake org, second org", "absorbing org", Time.zone.today)
+
+          merging_organisation_too.users.each do |user|
+            expect(MergeCompletionMailer).not_to receive(:send_absorbing_organisation_success_mail).with(user.email, "second org", "absorbing org", Time.zone.today)
+          end
+
+          merge_organisations_service.call
+        end
       end
 
       context "and merging organisation relationships" do