diff --git a/config.yaml b/config.yaml
index 0358db9..f31a09c 100644
--- a/config.yaml
+++ b/config.yaml
@@ -84,8 +84,7 @@
   # because of a large media file
   media_timeout: 0
 
-
-  ## Even more options (obscure use cases, detailed preferences) ##
+  ## Advanced behavior settings ##
 
   # Replacement string for the characters in dialog names which are potentially
   # problematic in filenames
diff --git a/dumpers/bare/dumper.rb b/dumpers/bare/dumper.rb
index bb07ce5..ec825ff 100644
--- a/dumpers/bare/dumper.rb
+++ b/dumpers/bare/dumper.rb
@@ -1,20 +1,13 @@
-require_relative '../dumper_interface'
+require_relative '../single_file_line_dumper'
 
-class BareDumper < DumperInterface
-
-  def start_dialog(dialog)
-    safe_name = get_safe_name(dialog['print_name'])
-    outfile = File.join(get_backup_dir, safe_name + '.txt')
-    @stream = File.open(outfile, 'w')
-  end
+class BareDumper < SingleFileLineDumper
 
   def dump_msg(dialog, msg)
     @stream.puts(msg['text']) if msg['text']
   end
 
-  def end_dialog(dialog)
-    @stream.close
-    @stream = nil
+  def get_file_extension
+    '.txt'
   end
 
 end
diff --git a/dumpers/daily_file_dumper.rb b/dumpers/daily_file_dumper.rb
index e1c1dde..cadbe9c 100644
--- a/dumpers/daily_file_dumper.rb
+++ b/dumpers/daily_file_dumper.rb
@@ -4,7 +4,7 @@
 
 class DailyFileDumper < DumperInterface
 
-  def start_dialog(dialog)
+  def start_dialog(dialog, progress)
     @prev_date = nil
     @output_buf = []
     safe_name = get_safe_name(dialog['print_name'])
@@ -14,13 +14,15 @@ def start_dialog(dialog)
 
   def dump_msg(dialog, msg)
     date = msg['date']
-    return unless date
+    return false unless date
     date = Time.at(date).to_date
     flush(dialog) if date != @prev_date && !@output_buf.empty?
     @prev_date = date
+    true
   end
 
   def flush(dialog)
+    return if @output_buf.empty? || @prev_date.nil?
     filename = get_filename_for_date(dialog, @prev_date)
     path = File.join(@output_dir, filename)
     File.open(path, 'w') do |stream|
@@ -31,6 +33,7 @@ def flush(dialog)
 
   def end_dialog(dialog)
     flush(dialog)
+    nil
   end
 
   def get_filename_for_date(dialog, date)
diff --git a/dumpers/dumper_interface.rb b/dumpers/dumper_interface.rb
index 4d03af6..64f1521 100644
--- a/dumpers/dumper_interface.rb
+++ b/dumpers/dumper_interface.rb
@@ -11,7 +11,7 @@
 # * lib/util.rb exports some useful helpers. For example get_backup_dir returns
 #   the output basedir path
 # * The same Dumper instance will be used for all dialogs in a backup session
-# * $config contains a hash of options parsed from config.json5
+# * $config contains a hash of options parsed from the configuration file
 #   (which is possibly interesting for custom dumper-specific options)
 
 class DumperInterface
@@ -23,20 +23,31 @@ def start_backup
   end
 
   # Will be called just before dumping a dialog's messages
-  def start_dialog(dialog)
-    # dialog: Hash
+  def start_dialog(dialog, progress)
+    # dialog: Hash, progress: DumpProgress
     nil
   end
 
+  # Will be called before each message to dump, to determine whether it is new
+  # enough to back up
+  # This default makes sense in simple cases, override for advanced custom logic
+  def msg_fresh?(msg, progress)
+    # msg: Hash, progress: DumpProgress
+    !progress.last_id || msg['id'] > progress.last_id
+  end
+
   # Will be called for each message to dump (from newest to oldest)
   # See the python binding documentation to get an idea of the msg attributes:
   # https://github.com/vysheng/tg/blob/master/README-PY.md#attributes-1
+  # Returning boolean false causes an early abort (skips to the next dialog)
   def dump_msg(dialog, msg)
     # dialog, msg: Hash
     raise 'dump_msg must be implemented'
   end
 
   # Will be called just after dumping a dialog's messages
+  # Optionally return a hash with state information that will be saved as
+  # custom progress data
   # dialog: Hash
   def end_dialog(dialog)
     # dialog: Hash
diff --git a/dumpers/json/dumper.rb b/dumpers/json/dumper.rb
index 9ab059b..f259e4f 100644
--- a/dumpers/json/dumper.rb
+++ b/dumpers/json/dumper.rb
@@ -1,21 +1,14 @@
 require 'json'
-require_relative '../dumper_interface'
+require_relative '../single_file_line_dumper'
 
-class JsonDumper < DumperInterface
-
-  def start_dialog(dialog)
-    safe_name = get_safe_name(dialog['print_name'])
-    outfile = File.join(get_backup_dir, safe_name + '.jsonl')
-    @stream = File.open(outfile, 'w')
-  end
+class JsonDumper < SingleFileLineDumper
 
   def dump_msg(dialog, msg)
     @stream.puts(JSON.generate(msg))
   end
 
-  def end_dialog(dialog)
-    @stream.close
-    @stream = nil
+  def get_file_extension
+    '.jsonl'
   end
 
 end
diff --git a/dumpers/pisg/dumper.rb b/dumpers/pisg/dumper.rb
index f2feff6..f557c7a 100644
--- a/dumpers/pisg/dumper.rb
+++ b/dumpers/pisg/dumper.rb
@@ -3,7 +3,7 @@
 
 class PisgDumper < DailyFileDumper
 
-  def start_dialog(dialog)
+  def start_dialog(dialog, progress)
     super
     @users = {}
     @oldest_message_date = nil
@@ -34,11 +34,13 @@ def end_dialog(dialog)
       path = File.join(@output_dir, 'oldest_message_date')
       File.open(path, 'w') {|f| f.write(@oldest_message_date.utc.iso8601) }
     end
+
+    nil
   end
 
   def dump_msg(dialog, msg)
-    super
-    return unless msg['date'] and msg['from']
+    return unless super
+    return unless msg['from']
     return if msg['from']['print_name'].to_s == ''
     @oldest_message_date = Time.at(msg['date'])
     @users[msg['from']['id']] = msg['from']
diff --git a/dumpers/plaintext/dumper.rb b/dumpers/plaintext/dumper.rb
index 2181fef..a923099 100644
--- a/dumpers/plaintext/dumper.rb
+++ b/dumpers/plaintext/dumper.rb
@@ -3,7 +3,7 @@
 class PlaintextDumper < DailyFileDumper
 
   def dump_msg(dialog, msg)
-    super
+    return unless super
     date_str = Time.at(msg['date']).strftime('[%s] ' % $config['date_format'])
     from_name = get_full_name(msg['from'])
 
diff --git a/dumpers/single_file_line_dumper.rb b/dumpers/single_file_line_dumper.rb
new file mode 100644
index 0000000..5eddad4
--- /dev/null
+++ b/dumpers/single_file_line_dumper.rb
@@ -0,0 +1,29 @@
+require_relative 'dumper_interface'
+
+class SingleFileLineDumper < DumperInterface
+
+  def start_dialog(dialog, progress)
+    @state = progress.dumper_state ? progress.dumper_state.clone : {}
+    outfile = @state['outfile']
+    if outfile
+      @prepender = DumpPrepender.new(outfile)
+    else
+      safe_name = get_safe_name(dialog['print_name'])
+      outfile = File.join(get_backup_dir, safe_name + get_file_extension)
+      @state['outfile'] = outfile
+    end
+    @stream = File.open(outfile, 'w')
+  end
+
+  def end_dialog(dialog)
+    @stream.close
+    @stream = nil
+    @prepender.merge if @prepender
+    @state
+  end
+
+  def get_file_extension
+    raise 'get_file_extension must be implemented'
+  end
+
+end
diff --git a/lib/dump_prepender.rb b/lib/dump_prepender.rb
new file mode 100644
index 0000000..d5fc55c
--- /dev/null
+++ b/lib/dump_prepender.rb
@@ -0,0 +1,18 @@
+require 'fileutils'
+
+class DumpPrepender
+
+  def initialize(filename)
+    @mainfile = filename
+    @tmpfile = filename + '.old'
+    FileUtils.mv(@mainfile, @tmpfile)
+  end
+
+  def merge
+    File.open(@mainfile, 'a') do |outstream|
+      IO.copy_stream(@tmpfile, outstream)
+    end
+    File.delete(@tmpfile)
+  end
+
+end
diff --git a/lib/dump_progress.rb b/lib/dump_progress.rb
new file mode 100644
index 0000000..994e268
--- /dev/null
+++ b/lib/dump_progress.rb
@@ -0,0 +1,40 @@
+require 'json'
+
+class DumpProgress
+
+  attr_reader :last_id
+  attr_reader :last_date
+  attr_reader :dumper_state
+  attr_writer :dumper_state
+
+  def initialize(last_id = nil, last_date = nil, dumper_state = {})
+    @last_id = last_id
+    @last_date = last_date
+    @dumper_state = dumper_state
+  end
+
+  def self.from_hash(hash)
+    self.new(hash['last_id'], hash['last_date'], hash['dumper_state'])
+  end
+
+  def to_hash
+    {
+      :last_id => @last_id,
+      :last_date => @last_date,
+      :dumper_state => @dumper_state
+    }
+  end
+
+  def to_json(*a)
+    to_hash.to_json(*a)
+  end
+
+  def bump_id(id)
+    @last_id = id if !@last_id || id > @last_id
+  end
+
+  def bump_date(date)
+    @last_date = date if !@last_date || date > @last_date
+  end
+
+end
diff --git a/lib/util.rb b/lib/util.rb
index 997aa12..e9a3dbf 100644
--- a/lib/util.rb
+++ b/lib/util.rb
@@ -1,3 +1,5 @@
+require_relative './dump_prepender'
+
 def get_safe_name(name)
   name.gsub(/([\/\\<>:"|?*]|[^\u0021-\uFFFF])/, $config['character_substitute'])
 end
diff --git a/telegram-history-dump.rb b/telegram-history-dump.rb
index 7ae7c96..aeeb949 100755
--- a/telegram-history-dump.rb
+++ b/telegram-history-dump.rb
@@ -2,12 +2,13 @@
 
 require 'fileutils'
 require 'json'
-require 'socket'
 require 'logger'
+require 'socket'
 require 'timeout'
 require 'yaml'
-require_relative 'lib/util'
 require_relative 'lib/cli_parser'
+require_relative 'lib/dump_progress'
+require_relative 'lib/util'
 
 cli_opts = CliParser.parse(ARGV)
 
@@ -38,7 +39,10 @@ def dump_dialog(dialog)
   if $config['download_media'].values.any? && $config['copy_media']
     FileUtils.mkdir_p(get_media_dir(dialog))
   end
-  $dumper.start_dialog(dialog)
+  id_str = dialog['id'].to_s
+  old_progress = $progress_snapshot[id_str] || DumpProgress.new
+  cur_progress = ($progress[id_str] ||= DumpProgress.new)
+  $dumper.start_dialog(dialog, old_progress)
   filter_regex = $config['filter_regex'] && eval($config['filter_regex'])
   offset = 0
   keep_dumping = true
@@ -55,11 +59,38 @@ def dump_dialog(dialog)
     end
     raise 'Expected array' unless msg_chunk.is_a?(Array)
     msg_chunk.reverse_each do |msg|
-      $log.warn('Message without date: %s' % msg) unless msg['date']
-      unless msg['text'] && filter_regex && filter_regex =~ msg['text']
+      dump_msg = true
+      if msg['id']
+        cur_progress.bump_id(msg['id'])
+      else
+        $log.warn('Dropping message without id: %s' % msg)
+        dump_msg = false
+      end
+      if msg['date']
+        cur_progress.bump_date(msg['date'])
+      else
+        $log.warn('Message without date: %s' % msg)
+      end
+
+      if msg['text'] && filter_regex && filter_regex =~ msg['text']
+        dump_msg = false
+      end
+
+      unless $dumper.msg_fresh?(msg, old_progress)
+        if keep_dumping
+          $log.info('Reached end of new messages since last backup')
+        end
+        dump_msg = false
+        keep_dumping = false
+      end
+
+      if dump_msg
         process_media(dialog, msg)
-        $dumper.dump_msg(dialog, msg)
+        if $dumper.dump_msg(dialog, msg) == false
+          keep_dumping = false
+        end
       end
+
       offset += 1
       if $config['backlog_limit'] > 0 && offset >= $config['backlog_limit']
         keep_dumping = false
@@ -69,7 +100,8 @@ def dump_dialog(dialog)
     keep_dumping = false if msg_chunk.length < $config['chunk_size']
     sleep($config['chunk_delay']) if keep_dumping
   end
-  $dumper.end_dialog(dialog)
+  state = $dumper.end_dialog(dialog) || {}
+  cur_progress.dumper_state=(state)
 end
 
 def process_media(dialog, msg)
@@ -148,6 +180,21 @@ def format_dialog_list(dialogs)
 
 FileUtils.mkdir_p(get_backup_dir)
 
+$progress = {}
+$progress_snapshot = {}
+progress_file = File.join(get_backup_dir, 'progress.json')
+progress_json = File.exists?(progress_file) ? File.read(progress_file) : '{}'
+progress_hash = JSON.parse(progress_json)
+if progress_hash['dumper'] && progress_hash['dumper'] != $config['dumper']
+  raise 'Dumper conflict: configured for "%s" but progress file reads "%s". '\
+   'Either use the same dumper or delete the output directory.'\
+  % [progress_hash['dumper'], $config['dumper']]
+end
+(progress_hash['dialogs'] || {}).each do |k,v|
+  $progress[k] = DumpProgress.from_hash(v)
+  $progress_snapshot[k] = DumpProgress.from_hash(v)
+end
+
 $log.info('Loading dumper module \'%s\'' % $config['dumper'])
 require_relative 'dumpers/%s/dumper.rb' % $config['dumper']
 $dumper = Dumper.new
@@ -190,6 +237,14 @@ def format_dialog_list(dialogs)
   end
 end
 
+$log.info('Saving progress file')
+progress_hash = {
+  :dumper => $config['dumper'],
+  :dialogs => $progress
+}
+progress_json = JSON.pretty_generate(progress_hash) + "\n"
+File.write(progress_file, progress_json)
+
 $dumper.end_backup
 if cli_opts.kill_tg
   connect_socket