diff --git a/Gemfile b/Gemfile
index 906b0f3aa23..a3222a8b26c 100644
--- a/Gemfile
+++ b/Gemfile
@@ -190,4 +190,5 @@ gem 'sassc', require: false
 if ENV["IMPORT"] == "1"
   gem 'mysql2'
   gem 'redcarpet'
+  gem 'sqlite3', '~> 1.3.13'
 end
diff --git a/lib/email/receiver.rb b/lib/email/receiver.rb
index eba4409dd09..75fb3e9bfc7 100644
--- a/lib/email/receiver.rb
+++ b/lib/email/receiver.rb
@@ -28,6 +28,9 @@ module Email
     class InvalidPostAction            < ProcessingError; end
 
     attr_reader :incoming_email
+    attr_reader :raw_email
+    attr_reader :mail
+    attr_reader :message_id
 
     def initialize(mail_string)
       raise EmptyEmailError if mail_string.blank?
@@ -241,7 +244,7 @@ module Email
 
     def try_to_encode(string, encoding)
       encoded = string.encode("UTF-8", encoding)
-      encoded.present? && encoded.valid_encoding? ? encoded : nil
+      !encoded.nil? && encoded.valid_encoding? ? encoded : nil
     rescue Encoding::InvalidByteSequenceError,
            Encoding::UndefinedConversionError,
            Encoding::ConverterNotFoundError
@@ -622,10 +625,7 @@ module Email
 
       # only add elided part in messages
       if options[:elided].present? && (SiteSetting.always_show_trimmed_content || is_private_message)
-        options[:raw] << "\n\n" << "<details class='elided'>" << "\n"
-        options[:raw] << "<summary title='#{I18n.t('emails.incoming.show_trimmed_content')}'>&#183;&#183;&#183;</summary>" << "\n"
-        options[:raw] << options[:elided] << "\n"
-        options[:raw] << "</details>" << "\n"
+        options[:raw] << Email::Receiver.elided_html(options[:elided])
       end
 
       user = options.delete(:user)
@@ -643,6 +643,14 @@ module Email
       result.post
     end
 
+    def self.elided_html(elided)
+      html =  "\n\n" << "<details class='elided'>" << "\n"
+      html << "<summary title='#{I18n.t('emails.incoming.show_trimmed_content')}'>&#183;&#183;&#183;</summary>" << "\n"
+      html << elided << "\n"
+      html << "</details>" << "\n"
+      html
+    end
+
     def add_other_addresses(topic, sender)
       %i(to cc bcc).each do |d|
         if @mail[d] && @mail[d].address_list && @mail[d].address_list.addresses
diff --git a/script/import_scripts/mbox-experimental.rb b/script/import_scripts/mbox-experimental.rb
new file mode 100644
index 00000000000..065b0111bd8
--- /dev/null
+++ b/script/import_scripts/mbox-experimental.rb
@@ -0,0 +1,17 @@
+if ARGV.length != 1 || !File.exists?(ARGV[0])
+  STDERR.puts '', 'Usage of mbox importer:', 'bundle exec ruby mbox-experimental.rb <path/to/settings.yml>'
+  STDERR.puts '', "Use the settings file from #{File.expand_path('mbox/settings.yml', File.dirname(__FILE__))} as an example."
+  exit 1
+end
+
+module ImportScripts
+  module Mbox
+    require_relative 'mbox/support/settings'
+
+    @settings = Settings.load(ARGV[0])
+
+    require_relative 'mbox/importer'
+    Importer.new(@settings).perform
+  end
+end
+
diff --git a/script/import_scripts/mbox/importer.rb b/script/import_scripts/mbox/importer.rb
new file mode 100644
index 00000000000..762c162e823
--- /dev/null
+++ b/script/import_scripts/mbox/importer.rb
@@ -0,0 +1,161 @@
+require_relative '../base'
+require_relative 'support/database'
+require_relative 'support/indexer'
+require_relative 'support/settings'
+
+module ImportScripts::Mbox
+  class Importer < ImportScripts::Base
+    # @param settings [ImportScripts::Mbox::Settings]
+    def initialize(settings)
+      @settings = settings
+      super()
+
+      @database = Database.new(@settings.data_dir, @settings.batch_size)
+    end
+
+    def change_site_settings
+      super
+
+      SiteSetting.enable_staged_users = true
+    end
+
+    protected
+
+    def execute
+      index_messages
+      import_categories
+      import_users
+      import_posts
+    end
+
+    def index_messages
+      puts '', 'creating index'
+      indexer = Indexer.new(@database, @settings)
+      indexer.execute
+    end
+
+    def import_categories
+      puts '', 'creating categories'
+      rows = @database.fetch_categories
+
+      create_categories(rows) do |row|
+        {
+          id: row['name'],
+          name: row['name']
+        }
+      end
+    end
+
+    def import_users
+      puts '', 'creating users'
+      total_count = @database.count_users
+      last_email = ''
+
+      batches do |offset|
+        rows, last_email = @database.fetch_users(last_email)
+        break if rows.empty?
+
+        next if all_records_exist?(:users, rows.map { |row| row['email'] })
+
+        create_users(rows, total: total_count, offset: offset) do |row|
+          {
+            id: row['email'],
+            email: row['email'],
+            name: row['name'],
+            trust_level: @settings.trust_level,
+            staged: true,
+            created_at: to_time(row['date_of_first_message'])
+          }
+        end
+      end
+    end
+
+    def batches
+      super(@settings.batch_size)
+    end
+
+    def import_posts
+      puts '', 'creating topics and posts'
+      total_count = @database.count_messages
+      last_row_id = 0
+
+      batches do |offset|
+        rows, last_row_id = @database.fetch_messages(last_row_id)
+        break if rows.empty?
+
+        next if all_records_exist?(:posts, rows.map { |row| row['msg_id'] })
+
+        create_posts(rows, total: total_count, offset: offset) do |row|
+          if row['in_reply_to'].blank?
+            map_first_post(row)
+          else
+            map_reply(row)
+          end
+        end
+      end
+    end
+
+    def map_post(row)
+      user_id = user_id_from_imported_user_id(row['from_email']) || Discourse::SYSTEM_USER_ID
+      body = row['body'] || ''
+      body << map_attachments(row['raw_message'], user_id) if row['attachment_count'].positive?
+      body << Email::Receiver.elided_html(row['elided']) if row['elided'].present?
+
+      {
+        id: row['msg_id'],
+        user_id: user_id,
+        created_at: to_time(row['email_date']),
+        raw: body,
+        raw_email: row['raw_message'],
+        via_email: true,
+        # cook_method: Post.cook_methods[:email] # this is slowing down the import by factor 4
+      }
+    end
+
+    def map_first_post(row)
+      mapped = map_post(row)
+      mapped[:category] = category_id_from_imported_category_id(row['category'])
+      mapped[:title] = row['subject'].strip[0...255]
+      mapped
+    end
+
+    def map_reply(row)
+      parent = @lookup.topic_lookup_from_imported_post_id(row['in_reply_to'])
+
+      if parent.blank?
+        puts "Parent message #{row['in_reply_to']} doesn't exist. Skipping #{row['msg_id']}: #{row['subject'][0..40]}"
+        return nil
+      end
+
+      mapped = map_post(row)
+      mapped[:topic_id] = parent[:topic_id]
+      mapped
+    end
+
+    def map_attachments(raw_message, user_id)
+      receiver = Email::Receiver.new(raw_message)
+      attachment_markdown = ''
+
+      receiver.attachments.each do |attachment|
+        tmp = Tempfile.new(['discourse-email-attachment', File.extname(attachment.filename)])
+
+        begin
+          File.open(tmp.path, 'w+b') { |f| f.write attachment.body.decoded }
+          upload = UploadCreator.new(tmp, attachment.filename).create_for(user_id)
+
+          if upload && upload.errors.empty?
+            attachment_markdown << "\n\n#{receiver.attachment_markdown(upload)}\n\n"
+          end
+        ensure
+          tmp.try(:close!)
+        end
+      end
+
+      attachment_markdown
+    end
+
+    def to_time(datetime)
+      Time.zone.at(DateTime.iso8601(datetime)) if datetime
+    end
+  end
+end
diff --git a/script/import_scripts/mbox/settings.yml b/script/import_scripts/mbox/settings.yml
new file mode 100644
index 00000000000..0a193aa1ed0
--- /dev/null
+++ b/script/import_scripts/mbox/settings.yml
@@ -0,0 +1,9 @@
+# PostgreSQL mailing lists
+#data_dir: /data/import/postgres
+#split_regex: "^From .*@postgresql.org.*"
+
+# ruby-talk mailing list
+data_dir: /data/import/ruby-talk/news/gmane/comp/lang/ruby
+split_regex: ""
+
+default_trust_level: 1
diff --git a/script/import_scripts/mbox/support/database.rb b/script/import_scripts/mbox/support/database.rb
new file mode 100644
index 00000000000..396d23e5b23
--- /dev/null
+++ b/script/import_scripts/mbox/support/database.rb
@@ -0,0 +1,261 @@
+require 'sqlite3'
+
+module ImportScripts::Mbox
+  class Database
+    SCHEMA_VERSION = 1
+
+    def initialize(directory, batch_size)
+      @db = SQLite3::Database.new("#{directory}/index.db", results_as_hash: true)
+      @batch_size = batch_size
+
+      configure_database
+      upgrade_schema_version
+      create_table_for_categories
+      create_table_for_imported_files
+      create_table_for_emails
+      create_table_for_replies
+      create_table_for_users
+    end
+
+    def insert_category(category)
+      @db.execute(<<-SQL, category)
+        INSERT OR REPLACE INTO category (name, description)
+        VALUES (:name, :description)
+      SQL
+    end
+
+    def insert_imported_file(imported_file)
+      @db.execute(<<-SQL, imported_file)
+        INSERT OR REPLACE INTO imported_file (category, filename, checksum)
+        VALUES (:category, :filename, :checksum)
+      SQL
+    end
+
+    def insert_email(email)
+      @db.execute(<<-SQL, email)
+        INSERT OR REPLACE INTO email (msg_id, from_email, from_name, subject,
+          email_date, raw_message, body, elided, attachment_count, charset,
+          category, filename, first_line_number, last_line_number)
+        VALUES (:msg_id, :from_email, :from_name, :subject,
+          :email_date, :raw_message, :body, :elided, :attachment_count, :charset,
+          :category, :filename, :first_line_number, :last_line_number)
+      SQL
+    end
+
+    def insert_replies(msg_id, reply_message_ids)
+      sql = <<-SQL
+        INSERT OR REPLACE INTO reply (msg_id, in_reply_to)
+        VALUES (:msg_id, :in_reply_to)
+      SQL
+
+      @db.prepare(sql) do |stmt|
+        reply_message_ids.each do |in_reply_to|
+          stmt.execute(msg_id, in_reply_to)
+        end
+      end
+    end
+
+    def update_in_reply_to_of_emails
+      @db.execute <<-SQL
+        UPDATE email
+        SET in_reply_to = (
+          SELECT e.msg_id
+          FROM reply r
+            JOIN email e ON (r.in_reply_to = e.msg_id)
+          WHERE r.msg_id = email.msg_id
+          ORDER BY e.email_date DESC
+          LIMIT 1
+        )
+      SQL
+    end
+
+    def sort_emails
+      @db.execute 'DELETE FROM email_order'
+
+      @db.execute <<-SQL
+        WITH RECURSIVE
+          messages(msg_id, level, email_date) AS (
+            SELECT msg_id, 0 AS level, email_date
+            FROM email
+            WHERE in_reply_to IS NULL
+            UNION ALL
+            SELECT e.msg_id, m.level + 1, e.email_date
+            FROM email e
+              JOIN messages m ON e.in_reply_to = m.msg_id
+            ORDER BY level, email_date, msg_id
+          )
+        INSERT INTO email_order (msg_id)
+        SELECT msg_id
+        FROM messages
+      SQL
+    end
+
+    def fill_users_from_emails
+      @db.execute 'DELETE FROM user'
+
+      @db.execute <<-SQL
+        INSERT INTO user (email, name, date_of_first_message)
+        SELECT from_email, MIN(from_name) AS from_name, MIN(email_date)
+        FROM email
+        WHERE from_email IS NOT NULL
+        GROUP BY from_email
+        ORDER BY from_email
+      SQL
+    end
+
+    def fetch_imported_files(category)
+      @db.execute(<<-SQL, category)
+        SELECT filename, checksum
+        FROM imported_file
+        WHERE category = :category
+      SQL
+    end
+
+    def fetch_categories
+      @db.execute <<-SQL
+        SELECT name, description
+        FROM category
+        ORDER BY name
+      SQL
+    end
+
+    def count_users
+      @db.get_first_value <<-SQL
+        SELECT COUNT(*)
+        FROM user
+      SQL
+    end
+
+    def fetch_users(last_email)
+      rows = @db.execute(<<-SQL, last_email)
+        SELECT email, name, date_of_first_message
+        FROM user
+        WHERE email > :last_email
+        LIMIT #{@batch_size}
+      SQL
+
+      add_last_column_value(rows, 'email')
+    end
+
+    def count_messages
+      @db.get_first_value <<-SQL
+        SELECT COUNT(*)
+        FROM email
+        WHERE email_date IS NOT NULL
+      SQL
+    end
+
+    def fetch_messages(last_row_id)
+      rows = @db.execute(<<-SQL, last_row_id)
+        SELECT o.ROWID, e.msg_id, from_email, subject, email_date, in_reply_to,
+          raw_message, body, elided, attachment_count, category
+        FROM email e
+          JOIN email_order o USING (msg_id)
+        WHERE email_date IS NOT NULL AND
+          o.ROWID > :last_row_id
+        ORDER BY o.ROWID
+        LIMIT #{@batch_size}
+      SQL
+
+      add_last_column_value(rows, 'rowid')
+    end
+
+    private
+
+    def configure_database
+      @db.execute 'PRAGMA journal_mode = TRUNCATE'
+    end
+
+    def upgrade_schema_version
+      # current_version = query("PRAGMA user_version").last[0]
+      @db.execute "PRAGMA user_version = #{SCHEMA_VERSION}"
+    end
+
+    def create_table_for_categories
+      @db.execute <<-SQL
+        CREATE TABLE IF NOT EXISTS category (
+          name TEXT NOT NULL PRIMARY KEY,
+          description TEXT
+        )
+      SQL
+    end
+
+    def create_table_for_imported_files
+      @db.execute <<-SQL
+        CREATE TABLE IF NOT EXISTS imported_file (
+          category TEXT NOT NULL,
+          filename TEXT NOT NULL,
+          checksum TEXT NOT NULL,
+          PRIMARY KEY (category, filename),
+          FOREIGN KEY(category) REFERENCES category(name)
+        )
+      SQL
+    end
+
+    def create_table_for_emails
+      @db.execute <<-SQL
+        CREATE TABLE IF NOT EXISTS email (
+          msg_id TEXT NOT NULL PRIMARY KEY,
+          from_email TEXT,
+          from_name TEXT,
+          subject TEXT,
+          in_reply_to TEXT,
+          email_date DATETIME,
+          raw_message TEXT,
+          body TEXT,
+          elided TEXT,
+          attachment_count INTEGER NOT NULL DEFAULT 0,
+          charset TEXT,
+          category TEXT NOT NULL,
+          filename TEXT NOT NULL,
+          first_line_number INTEGER,
+          last_line_number INTEGER,
+          FOREIGN KEY(category) REFERENCES category(name)
+        )
+      SQL
+
+      @db.execute 'CREATE INDEX IF NOT EXISTS email_by_from ON email (from_email)'
+      @db.execute 'CREATE INDEX IF NOT EXISTS email_by_in_reply_to ON email (in_reply_to)'
+      @db.execute 'CREATE INDEX IF NOT EXISTS email_by_date ON email (email_date)'
+
+      @db.execute <<-SQL
+        CREATE TABLE IF NOT EXISTS email_order (
+          msg_id TEXT NOT NULL PRIMARY KEY
+        )
+      SQL
+    end
+
+    def create_table_for_replies
+      @db.execute <<-SQL
+        CREATE TABLE IF NOT EXISTS reply (
+          msg_id TEXT NOT NULL,
+          in_reply_to TEXT NOT NULL,
+          PRIMARY KEY (msg_id, in_reply_to),
+          FOREIGN KEY(msg_id) REFERENCES email(msg_id)
+        )
+      SQL
+
+      @db.execute 'CREATE INDEX IF NOT EXISTS reply_by_in_reply_to ON reply (in_reply_to)'
+    end
+
+    def create_table_for_users
+      @db.execute <<-SQL
+        CREATE TABLE IF NOT EXISTS user (
+          email TEXT NOT NULL PRIMARY KEY,
+          name TEXT,
+          date_of_first_message DATETIME NOT NULL
+        )
+      SQL
+    end
+
+    def add_last_column_value(rows, *last_columns)
+      return rows if last_columns.empty?
+
+      result = [rows]
+      last_row = rows.last
+
+      last_columns.each { |column| result.push(last_row ? last_row[column] : nil) }
+      result
+    end
+  end
+end
diff --git a/script/import_scripts/mbox/support/indexer.rb b/script/import_scripts/mbox/support/indexer.rb
new file mode 100644
index 00000000000..4884365a062
--- /dev/null
+++ b/script/import_scripts/mbox/support/indexer.rb
@@ -0,0 +1,226 @@
+require_relative 'database'
+require 'json'
+require 'yaml'
+
+module ImportScripts::Mbox
+  class Indexer
+    # @param database [ImportScripts::Mbox::Database]
+    # @param settings [ImportScripts::Mbox::Settings]
+    def initialize(database, settings)
+      @database = database
+      @root_directory = settings.data_dir
+      @split_regex = settings.split_regex
+    end
+
+    def execute
+      directories = Dir.glob(File.join(@root_directory, '*'))
+      directories.select! { |f| File.directory?(f) }
+      directories.sort!
+
+      directories.each do |directory|
+        puts "indexing files in #{directory}"
+        category = index_category(directory)
+        index_emails(directory, category[:name])
+      end
+
+      puts '', 'indexing replies and users'
+      @database.update_in_reply_to_of_emails
+      @database.sort_emails
+      @database.fill_users_from_emails
+    end
+
+    private
+
+    METADATA_FILENAME = 'metadata.yml'.freeze
+
+    def index_category(directory)
+      metadata_file = File.join(directory, METADATA_FILENAME)
+
+      if File.exist?(metadata_file)
+        # workaround for YML files that contain classname in file header
+        yaml = File.read(metadata_file).sub(/^--- !.*$/, '---')
+        metadata = YAML.load(yaml)
+      else
+        metadata = {}
+      end
+
+      category = {
+        name: metadata['name'].presence || File.basename(directory),
+        description: metadata['description']
+      }
+
+      @database.insert_category(category)
+      category
+    end
+
+    def index_emails(directory, category_name)
+      all_messages(directory, category_name) do |receiver, filename, first_line_number, last_line_number|
+        msg_id = receiver.message_id
+        parsed_email = receiver.mail
+        from_email, from_display_name = receiver.parse_from_field(parsed_email)
+        body, elided = receiver.select_body
+        reply_message_ids = extract_reply_message_ids(parsed_email)
+
+        email = {
+          msg_id: msg_id,
+          from_email: from_email,
+          from_name: from_display_name,
+          subject: extract_subject(receiver, category_name),
+          email_date: parsed_email.date&.to_s,
+          raw_message: receiver.raw_email,
+          body: body,
+          elided: elided,
+          attachment_count: receiver.attachments.count,
+          charset: parsed_email.charset&.downcase,
+          category: category_name,
+          filename: File.basename(filename),
+          first_line_number: first_line_number,
+          last_line_number: last_line_number
+        }
+
+        @database.insert_email(email)
+        @database.insert_replies(msg_id, reply_message_ids) unless reply_message_ids.empty?
+      end
+    end
+
+    def imported_file_checksums(category_name)
+      rows = @database.fetch_imported_files(category_name)
+      rows.each_with_object({}) do |row, hash|
+        hash[row['filename']] = row['checksum']
+      end
+    end
+
+    def all_messages(directory, category_name)
+      checksums = imported_file_checksums(category_name)
+
+      Dir.foreach(directory) do |filename|
+        filename = File.join(directory, filename)
+        next if ignored_file?(filename, checksums)
+
+        puts "indexing #{filename}"
+
+        if @split_regex.present?
+          each_mail(filename) do |raw_message, first_line_number, last_line_number|
+            yield read_mail_from_string(raw_message), filename, first_line_number, last_line_number
+          end
+        else
+          yield read_mail_from_file(filename), filename
+        end
+
+        mark_as_fully_indexed(category_name, filename)
+      end
+    end
+
+    def mark_as_fully_indexed(category_name, filename)
+      imported_file = {
+        category: category_name,
+        filename: filename,
+        checksum: calc_checksum(filename)
+      }
+
+      @database.insert_imported_file(imported_file)
+    end
+
+    def each_mail(filename)
+      raw_message = ''
+      first_line_number = 1
+      last_line_number = 0
+
+      each_line(filename) do |line|
+        line = line.scrub
+
+        if line =~ @split_regex && last_line_number.positive?
+          yield raw_message, first_line_number, last_line_number
+          raw_message = ''
+          first_line_number = last_line_number + 1
+        else
+          raw_message << line
+        end
+
+        last_line_number += 1
+      end
+
+      yield raw_message, first_line_number, last_line_number if raw_message.present?
+    end
+
+    def each_line(filename)
+      raw_file = File.open(filename, 'r')
+      text_file = filename.end_with?('.gz') ? Zlib::GzipReader.new(raw_file) : raw_file
+
+      text_file.each_line do |line|
+        yield line
+      end
+    ensure
+      raw_file.close if raw_file
+    end
+
+    def read_mail_from_file(filename)
+      raw_message = File.read(filename)
+      read_mail_from_string(raw_message)
+    end
+
+    def read_mail_from_string(raw_message)
+      Email::Receiver.new(raw_message)
+    end
+
+    def extract_reply_message_ids(mail)
+      message_ids = [mail.in_reply_to, Email::Receiver.extract_references(mail.references)]
+      message_ids.flatten!
+      message_ids.select!(&:present?)
+      message_ids.uniq!
+      message_ids.first(20)
+    end
+
+    def extract_subject(receiver, list_name)
+      subject = receiver.subject
+      return nil if subject.blank?
+
+      # TODO: make the list name (or maybe multiple names) configurable
+      # Strip mailing list name from subject
+      subject = subject.gsub(/\[#{Regexp.escape(list_name)}\]/, '').strip
+
+      clean_subject(subject)
+    end
+
+    # TODO: refactor and move prefixes to settings
+    def clean_subject(subject)
+      original_length = subject.length
+
+      # Strip Reply prefix from title (Standard and localized)
+      subject = subject.gsub(/^Re: */i, '')
+      subject = subject.gsub(/^R: */i, '') #Italian
+      subject = subject.gsub(/^RIF: */i, '') #Italian
+
+      # Strip Forward prefix from title (Standard and localized)
+      subject = subject.gsub(/^Fwd: */i, '')
+      subject = subject.gsub(/^I: */i, '') #Italian
+
+      subject.strip
+
+      # In case of mixed localized prefixes there could be many of them
+      # if the mail client didn't strip the localized ones
+      if original_length > subject.length
+        clean_subject(subject)
+      else
+        subject
+      end
+    end
+
+    def ignored_file?(filename, checksums)
+      File.directory?(filename) || metadata_file?(filename) || fully_indexed?(filename, checksums)
+    end
+
+    def metadata_file?(filename)
+      File.basename(filename) == METADATA_FILENAME
+    end
+
+    def fully_indexed?(filename, checksums)
+      checksum = checksums[filename]
+      checksum.present? && calc_checksum(filename) == checksum
+    end
+
+    def calc_checksum(filename)
+      Digest::SHA256.file(filename).hexdigest
+    end
+  end
+end
diff --git a/script/import_scripts/mbox/support/settings.rb b/script/import_scripts/mbox/support/settings.rb
new file mode 100644
index 00000000000..79fb5ab56b6
--- /dev/null
+++ b/script/import_scripts/mbox/support/settings.rb
@@ -0,0 +1,22 @@
+require 'yaml'
+
+module ImportScripts::Mbox
+  class Settings
+    def self.load(filename)
+      yaml = YAML.load_file(filename)
+      Settings.new(yaml)
+    end
+
+    attr_reader :data_dir
+    attr_reader :split_regex
+    attr_reader :batch_size
+    attr_reader :trust_level
+
+    def initialize(yaml)
+      @data_dir = yaml['data_dir']
+      @split_regex = Regexp.new(yaml['split_regex']) unless yaml['split_regex'].empty?
+      @batch_size = 1000 # no need to make this actually configurable at the moment
+      @trust_level = yaml['default_trust_level']
+    end
+  end
+end