diff --git a/app/models/mail_handler.rb b/app/models/mail_handler.rb
index fd2e25fb5..4f9c73136 100644
--- a/app/models/mail_handler.rb
+++ b/app/models/mail_handler.rb
@@ -636,6 +636,9 @@ class MailHandler < ActionMailer::Base
 
     unless delimiters.empty?
       regex = Regexp.new("^(\\p{Space}|>)*(#{ Regexp.union(delimiters) })\\p{Space}*[\\r\\n].*", Regexp::MULTILINE)
+      if Setting.text_formatting == "common_mark" && Redmine::Configuration['common_mark_enable_hardbreaks'] == false
+        body = Redmine::WikiFormatting::CommonMark::AppendSpacesToLines.call(body)
+      end
       body = body.gsub(regex, '')
     end
     body.strip
diff --git a/app/views/settings/_general.html.erb b/app/views/settings/_general.html.erb
index b8d82486a..043067f18 100644
--- a/app/views/settings/_general.html.erb
+++ b/app/views/settings/_general.html.erb
@@ -22,7 +22,7 @@
 <p><%= setting_select :text_formatting, Redmine::WikiFormatting.formats_for_select, :blank => :label_none %>
   <span id="common_mark_info" class="<%= "hidden" unless Setting.text_formatting == "common_mark" %>">
     <label class="block">
-      <%= check_box_tag(nil, '', Redmine::Configuration['common_mark_enable_hardbreaks'] === true, disabled: true) %>
+      <%= check_box_tag(nil, '', Redmine::Configuration['common_mark_enable_hardbreaks'] == true, disabled: true) %>
       Hardbreaks
     </label>
     <em class="info">
diff --git a/lib/redmine/wiki_formatting/common_mark/append_spaces_to_lines.rb b/lib/redmine/wiki_formatting/common_mark/append_spaces_to_lines.rb
new file mode 100644
index 000000000..73c5a4177
--- /dev/null
+++ b/lib/redmine/wiki_formatting/common_mark/append_spaces_to_lines.rb
@@ -0,0 +1,30 @@
+# frozen_string_literal: true
+
+# Redmine - project management software
+# Copyright (C) 2006-2021  Jean-Philippe Lang
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+
+module Redmine
+  module WikiFormatting
+    module CommonMark
+      class AppendSpacesToLines
+        def self.call(string)
+          string&.gsub(/(?<!  |\\)(\r?\n)/, "  \\1")
+        end
+      end
+    end
+  end
+end
diff --git a/lib/redmine/wiki_formatting/common_mark/formatter.rb b/lib/redmine/wiki_formatting/common_mark/formatter.rb
index 3c2f3ad09..3a50f78a3 100644
--- a/lib/redmine/wiki_formatting/common_mark/formatter.rb
+++ b/lib/redmine/wiki_formatting/common_mark/formatter.rb
@@ -46,7 +46,7 @@ module Redmine
         ],
       }.freeze
 
-      if Redmine::Configuration['common_mark_enable_hardbreaks'] === true
+      if Redmine::Configuration['common_mark_enable_hardbreaks'] == true
         PIPELINE_CONFIG[:commonmarker_render_options].push(:HARDBREAKS)
       end
       PIPELINE_CONFIG[:commonmarker_render_options].freeze