diff --git a/app/models/channel/filter/internal_article_check.rb b/app/models/channel/filter/internal_article_check.rb
new file mode 100644
index 000000000..10e52145e
--- /dev/null
+++ b/app/models/channel/filter/internal_article_check.rb
@@ -0,0 +1,43 @@
+# Copyright (C) 2012-2016 Zammad Foundation, http://zammad-foundation.org/
+
+module Channel::Filter::InternalArticleCheck
+  def self.run(_channel, mail, _transaction_params)
+    return if mail[ :'x-zammad-ticket-id' ].blank?
+
+    ticket = Ticket.find_by(id: mail[ :'x-zammad-ticket-id' ])
+    return if ticket.blank?
+
+    return if !in_reply_to_is_internal?(mail, ticket) &&
+              !last_outgoing_mail_is_internal?(mail, ticket)
+
+    mail[ :'x-zammad-article-internal' ] = true
+    true
+  end
+
+  def self.in_reply_to_is_internal?(mail, ticket)
+    return false if mail[:'in-reply-to'].blank?
+
+    message_id_md5 = Digest::MD5.hexdigest(mail[:'in-reply-to'])
+    ticket.articles.exists?(message_id_md5: message_id_md5, internal: true)
+  end
+
+  def self.last_outgoing_mail_is_internal?(mail, ticket)
+    return false if mail[:'in-reply-to'].present?
+
+    from_email = parse_email(mail[:from_email])
+    return false if from_email.blank?
+
+    last_outgoing_mail = ticket.articles
+      .where("ticket_articles.to #{Rails.application.config.db_like} ?", "%#{from_email}%")
+      .order(created_at: :desc).first
+
+    last_outgoing_mail&.internal.present?
+  end
+
+  def self.parse_email(email)
+    Mail::AddressList.new(email)&.addresses&.first&.address
+  rescue
+    Rails.logger.error "Can not parse email: #{email}"
+    nil
+  end
+end
diff --git a/db/migrate/202104070000001_setting_add_internal_article_check.rb b/db/migrate/202104070000001_setting_add_internal_article_check.rb
new file mode 100644
index 000000000..1b3f1a19b
--- /dev/null
+++ b/db/migrate/202104070000001_setting_add_internal_article_check.rb
@@ -0,0 +1,17 @@
+class SettingAddInternalArticleCheck < ActiveRecord::Migration[5.2]
+  def change
+
+    # return if it's a new setup
+    return if !Setting.exists?(name: 'system_init_done')
+
+    Setting.create_if_not_exists(
+      title:       'Define postmaster filter.',
+      name:        '5500_postmaster_internal_article_check',
+      area:        'Postmaster::PreFilter',
+      description: 'Defines the postmaster filter which set the article internal if a forwarded, replied or sent email also exists with the article internal received.',
+      options:     {},
+      state:       'Channel::Filter::InternalArticleCheck',
+      frontend:    false
+    )
+  end
+end
diff --git a/db/seeds/settings.rb b/db/seeds/settings.rb
index c3d26f774..cc46e45bf 100644
--- a/db/seeds/settings.rb
+++ b/db/seeds/settings.rb
@@ -3480,6 +3480,15 @@ Setting.create_if_not_exists(
   state:       'Channel::Filter::ServiceNowCheck',
   frontend:    false
 )
+Setting.create_if_not_exists(
+  title:       'Define postmaster filter.',
+  name:        '5500_postmaster_internal_article_check',
+  area:        'Postmaster::PreFilter',
+  description: 'Defines the postmaster filter which set the article internal if a forwarded, replied or sent email also exists with the article internal received.',
+  options:     {},
+  state:       'Channel::Filter::InternalArticleCheck',
+  frontend:    false
+)
 Setting.create_if_not_exists(
   title:       'Icinga integration',
   name:        'icinga_integration',
diff --git a/spec/models/channel/filter/internal_article_check_spec.rb b/spec/models/channel/filter/internal_article_check_spec.rb
new file mode 100644
index 000000000..27181534b
--- /dev/null
+++ b/spec/models/channel/filter/internal_article_check_spec.rb
@@ -0,0 +1,186 @@
+require 'rails_helper'
+
+RSpec.describe Channel::Filter::InternalArticleCheck do
+  let(:ticket) { create(:ticket) }
+  let(:vendor_email) { 'vendor@example.com' }
+  let(:article_to) { vendor_email }
+  let(:from) { "From: <#{vendor_email}>" }
+  let(:message_id) { 'some_message_id_999@example.com' }
+  let(:in_reply_to) { message_id }
+  let(:subject) { "Subject: #{ticket.subject_build('some subject')}" }
+  let(:ticket_article) { build(:ticket_article, ticket: ticket, to: article_to, internal: false, message_id: message_id) }
+  let(:inbound_email) { create(:ticket_article, :inbound_email, ticket: ticket) }
+  let(:outbound_email) { create(:ticket_article, :outbound_email, ticket: ticket) }
+  let(:internal_note) { create(:ticket_article, :outbound_note, ticket: ticket, internal: true) }
+
+  let(:email_raw_string) do
+    email_file_path = Rails.root.join('test/data/mail/mail001.box')
+    File.read(email_file_path)
+  end
+
+  let(:email_parse_mail_answer) do
+    channel_as_model = Channel.new(options: {})
+
+    email_raw_string.sub!(/^Subject: .+?$/, subject)
+    email_raw_string.sub!('From: <John.Smith@example.com>', from)
+    email_raw_string.sub!('Message-Id: <053EA3703574649ABDAF24D43A05604F327A130@MEMASFRK004.example.com>', "Message-Id: <053EA3703574649ABDAF24D43A05604F327A130@MEMASFRK004.example.com>\nIn-Reply-To: #{in_reply_to}")
+    Channel::EmailParser.new.process(channel_as_model, email_raw_string)
+  end
+
+  shared_examples 'setting new article to internal' do
+    it 'sets new article to internal' do
+      _ticket_p, article_p, _user_p = email_parse_mail_answer
+      expect(article_p.internal).to be true
+    end
+  end
+
+  shared_examples 'not setting new article to internal' do
+    it 'does not set new article to internal' do
+      _ticket_p, article_p, _user_p = email_parse_mail_answer
+      expect(article_p.internal).not_to be true
+    end
+  end
+
+  shared_examples 'sets new article to internal' do
+    context 'when From has email only' do
+      it_behaves_like 'setting new article to internal'
+    end
+
+    context 'when From have both name and email' do
+      let(:from) { "From: Some Vendor Name <#{vendor_email}>" }
+
+      it_behaves_like 'setting new article to internal'
+    end
+
+    context 'when From have name with brackets and email' do
+      let(:from) { "From: (Some Vendor Name) <#{vendor_email}>" }
+
+      it_behaves_like 'setting new article to internal'
+    end
+
+    context 'when From have name with brackets and uppercase email' do
+      let(:from) { "From: (Some Vendor Name) <#{vendor_email.upcase}>" }
+
+      it_behaves_like 'setting new article to internal'
+    end
+
+    context 'when From have name in quotes and email' do
+      let(:from) { "From: 'Günther John | Example GmbH' <#{vendor_email}>" }
+
+      it_behaves_like 'setting new article to internal'
+    end
+
+    context 'when From have email before name' do
+      let(:from) { "From: <#{vendor_email.upcase}> (Some Vendor Name)" }
+
+      it_behaves_like 'setting new article to internal'
+    end
+
+    context 'when article to have both name and email' do
+      let(:article_to) { "Some Vendor Name <#{vendor_email}>" }
+
+      it_behaves_like 'setting new article to internal'
+    end
+
+    context 'when article to have name with brackets and email' do
+      let(:article_to) { "(Some Vendor Name) <#{vendor_email}>" }
+
+      it_behaves_like 'setting new article to internal'
+    end
+
+    context 'when article to have name with brackets and uppercase email' do
+      let(:article_to) { "(Some Vendor Name) <#{vendor_email.upcase}>" }
+
+      it_behaves_like 'setting new article to internal'
+    end
+
+    context 'when article to have name in quotes and email' do
+      let(:article_to) { "'Günther John | Example GmbH' <#{vendor_email}>" }
+
+      it_behaves_like 'setting new article to internal'
+    end
+
+    context 'when article to have email before name' do
+      let(:article_to) { "<#{vendor_email}> (Some Vendor Name)" }
+
+      it_behaves_like 'setting new article to internal'
+    end
+  end
+
+  shared_examples 'checks in reply to header' do
+
+    context 'when associated article is internal' do
+      before { ticket_article.update! internal: true }
+
+      include_examples 'sets new article to internal'
+    end
+
+    context 'when there is no associated article' do
+      let(:article_to) { 'me@example.com' }
+
+      it_behaves_like 'not setting new article to internal'
+    end
+
+    context 'when associated article is not internal' do
+      before { ticket_article.update! internal: false }
+
+      it_behaves_like 'not setting new article to internal'
+    end
+
+  end
+
+  shared_examples 'checks last outgoing mail' do
+
+    context 'when associated article is internal' do
+      before { ticket_article.update! internal: true }
+
+      include_examples 'sets new article to internal'
+    end
+
+    context 'when there is no associated article' do
+      let(:article_to) { nil }
+
+      it_behaves_like 'not setting new article to internal'
+    end
+
+    context 'when associated article is not internal' do
+      before { ticket_article.update! internal: false }
+
+      it_behaves_like 'not setting new article to internal'
+    end
+
+    context 'when From have wrong email format' do
+      let(:from) { "From: 'Günther John | Example GmbH' <power quadrant #{vendor_email}>" }
+
+      it_behaves_like 'not setting new article to internal'
+    end
+
+    context 'when article to have wrong email format' do
+      let(:article_to) { "'Günther John | Example GmbH' <power quadrant #{vendor_email}>" }
+
+      it_behaves_like 'not setting new article to internal'
+    end
+
+    context 'when there is no article to can not be parsed' do
+      let(:article_to) { "From: (Some Vendor Name) <#{vendor_email.upcase}>" }
+
+      it_behaves_like 'not setting new article to internal'
+    end
+
+  end
+
+  describe '.run' do
+    before { inbound_email && outbound_email && internal_note }
+
+    context 'when in reply to header is present' do
+
+      include_examples 'checks in reply to header'
+    end
+
+    context 'when in reply to header is blank' do
+      let(:in_reply_to) { '' }
+
+      include_examples 'checks last outgoing mail'
+    end
+  end
+end