diff --git a/db/migrate/20210810091200_issue_3669_fix_domain.rb b/db/migrate/20210810091200_issue_3669_fix_domain.rb
new file mode 100644
index 000000000..cb6ebab64
--- /dev/null
+++ b/db/migrate/20210810091200_issue_3669_fix_domain.rb
@@ -0,0 +1,12 @@
+# Copyright (C) 2012-2021 Zammad Foundation, http://zammad-foundation.org/
+
+class Issue3669FixDomain < ActiveRecord::Migration[6.0]
+  def change
+    return if !Setting.exists?(name: 'system_init_done')
+
+    Channel.where(area: ['Google::Account', 'Microsoft365::Account']).each do |channel|
+      channel.options[:outbound][:options].delete(:domain)
+      channel.save!
+    end
+  end
+end
diff --git a/lib/external_credential/google.rb b/lib/external_credential/google.rb
index 5ea45c651..10de9ec88 100644
--- a/lib/external_credential/google.rb
+++ b/lib/external_credential/google.rb
@@ -57,7 +57,6 @@ class ExternalCredential::Google
         adapter: 'smtp',
         options: {
           host:           'smtp.gmail.com',
-          domain:         'gmail.com',
           port:           465,
           ssl:            true,
           user:           user_data[:email],
diff --git a/lib/external_credential/microsoft365.rb b/lib/external_credential/microsoft365.rb
index e74ec6145..ccf006341 100644
--- a/lib/external_credential/microsoft365.rb
+++ b/lib/external_credential/microsoft365.rb
@@ -61,7 +61,6 @@ class ExternalCredential::Microsoft365
         adapter: 'smtp',
         options: {
           host:           'smtp.office365.com',
-          domain:         'office365.com',
           port:           587,
           user:           user_data[:preferred_username],
           authentication: 'xoauth2',
diff --git a/spec/db/migrate/issue_3669_fix_domain_spec.rb b/spec/db/migrate/issue_3669_fix_domain_spec.rb
new file mode 100644
index 000000000..cc759a8cb
--- /dev/null
+++ b/spec/db/migrate/issue_3669_fix_domain_spec.rb
@@ -0,0 +1,49 @@
+# Copyright (C) 2012-2021 Zammad Foundation, http://zammad-foundation.org/
+
+require 'rails_helper'
+
+RSpec.describe Issue3669FixDomain, type: :db_migration do
+  let!(:channel) do
+    channel_options = {
+      inbound:  {
+        adapter: 'imap',
+        options: {
+          auth_type: 'XOAUTH2',
+          host:      'imap.gmail.com',
+          ssl:       true,
+          user:      'example@gmail.com',
+        },
+      },
+      outbound: {
+        adapter: 'smtp',
+        options: {
+          host:           'smtp.gmail.com',
+          domain:         'gmail.com',
+          port:           465,
+          ssl:            true,
+          user:           'example@gmail.com',
+          authentication: 'xoauth2',
+        },
+      },
+      auth:     {
+        provider:      'google',
+        type:          'XOAUTH2',
+        client_id:     'abc',
+        client_secret: 'efg',
+      },
+    }
+
+    Channel.create!(
+      area:          'Google::Account',
+      group_id:      Group.first.id,
+      options:       channel_options,
+      active:        false,
+      created_by_id: 1,
+      updated_by_id: 1,
+    )
+  end
+
+  it 'removes domain from the configuration' do
+    expect { migrate }.to change { channel.reload.options[:outbound][:options][:domain] }.to(nil)
+  end
+end
diff --git a/spec/factories/channel.rb b/spec/factories/channel.rb
index 821af32e5..2291f0aac 100644
--- a/spec/factories/channel.rb
+++ b/spec/factories/channel.rb
@@ -143,7 +143,6 @@ FactoryBot.define do
             'adapter' => 'smtp',
             'options' => {
               'host'           => 'smtp.gmail.com',
-              'domain'         => 'gmail.com',
               'port'           => 465,
               'ssl'            => true,
               'user'           => ENV['GMAIL_USER'],
@@ -186,7 +185,6 @@ FactoryBot.define do
             'adapter' => 'smtp',
             'options' => {
               'host'           => 'smtp.office365.com',
-              'domain'         => 'office365.com',
               'port'           => 587,
               'user'           => ENV['MICROSOFT365_USER'],
               'authentication' => 'xoauth2',
diff --git a/spec/lib/external_credential/google_spec.rb b/spec/lib/external_credential/google_spec.rb
index 135dc52af..17c222b02 100644
--- a/spec/lib/external_credential/google_spec.rb
+++ b/spec/lib/external_credential/google_spec.rb
@@ -129,7 +129,6 @@ RSpec.describe ExternalCredential::Google do
               'options' => a_hash_including(
                 'authentication' => 'xoauth2',
                 'host'           => 'smtp.gmail.com',
-                'domain'         => 'gmail.com',
                 'port'           => 465,
                 'ssl'            => true,
                 'user'           => primary_email,
diff --git a/spec/lib/external_credential/microsoft365_spec.rb b/spec/lib/external_credential/microsoft365_spec.rb
index d2c1df753..679962aa3 100644
--- a/spec/lib/external_credential/microsoft365_spec.rb
+++ b/spec/lib/external_credential/microsoft365_spec.rb
@@ -95,7 +95,6 @@ RSpec.describe ExternalCredential::Microsoft365 do
               'options' => a_hash_including(
                 'authentication' => 'xoauth2',
                 'host'           => 'smtp.office365.com',
-                'domain'         => 'office365.com',
                 'port'           => 587,
                 'user'           => email_address,
               )