Fixes #3096 - Japanese emails incorrectly converted

app/models/channel/email_parser.rb

@@ -528,14 +528,15 @@ process unprocessable_mails (tmp/unprocessable_mail/*.eml) again
 
   # https://github.com/zammad/zammad/issues/2922
   def force_parts_encoding_if_needed(mail)
-    mail.parts.each { |elem| force_single_part_encoding_if_needed(elem) }
+    # enforce encoding on both multipart parts and main body
+    ([mail] + mail.parts).each { |elem| force_single_part_encoding_if_needed(elem) }
   end
 
   # https://github.com/zammad/zammad/issues/2922
   def force_single_part_encoding_if_needed(part)
-    return if part.charset != 'iso-2022-jp'
+    return if part.charset&.downcase != 'iso-2022-jp'
 
-    part.body = part.body.encoded.unpack1('M').force_encoding('ISO-2022-JP').encode('UTF-8')
+    part.body = force_japanese_encoding part.body.encoded.unpack1('M')
   end
 
   ISO2022JP_REGEXP = /=\?ISO-2022-JP\?B\?(.+?)\?=/.freeze
@@ -543,7 +544,7 @@ process unprocessable_mails (tmp/unprocessable_mail/*.eml) again
   # https://github.com/zammad/zammad/issues/3115
   def header_field_unpack_japanese(field)
     field.value.gsub ISO2022JP_REGEXP do
-      Base64.decode64($1).force_encoding('SJIS').encode('UTF-8')
+      force_japanese_encoding Base64.decode64($1)
     end
   end
 
@@ -934,6 +935,16 @@ process unprocessable_mails (tmp/unprocessable_mail/*.eml) again
 
     "<gen-#{Digest::MD5.hexdigest(raw_message)}@#{fqdn}>"
   end
+
+  # https://github.com/zammad/zammad/issues/3096
+  # specific email needs to be forced to ISO-2022-JP
+  # but that breaks other emails that can be forced to SJIS only
+  # thus force to ISO-2022-JP but fallback to SJIS
+  def force_japanese_encoding(input)
+    input.force_encoding('ISO-2022-JP').encode('UTF-8')
+  rescue
+    input.force_encoding('SJIS').encode('UTF-8')
+  end
 end
 
 module Mail

test/data/mail/mail098.box

@@ -0,0 +1,18 @@
+Return-Path: <return@example.org>
+Delivered-To: delivered@example.org
+Received: from localhost (unknown [127.0.0.1])
+	by mail.example.org (Postfix) with ESMTP id 31337;
+	Mon, 21 Dec 2020 11:03:03 +0900 (JST)
+MIME-Version: 1.0
+Content-Type: text/plain; charset=ISO-2022-JP
+Content-Transfer-Encoding: 7bit
+From: "=?ISO-2022-JP?B?GyRCO3ZMMzZJGyhC==?="
+ <noreply@example.org>
+Reply-To: info@example.org
+To: noreply@example.org
+Cc: 
+Subject: =?ISO-2022-JP?B?GyRCMGxNdyFXJHIlIiVDJVckNyReJDkbKEI=?=
+Message-Id: <20201221110303>
+Date: Mon, 21 Dec 2020 11:33:03 +0900 (JST)
+
+$B%+%F%4%j!'A4%a%s%P!<(B

test/data/mail/mail098.yml

@@ -0,0 +1,13 @@
+--- !ruby/hash:ActiveSupport::HashWithIndifferentAccess
+from: '"事務局" <noreply@example.org>'
+from_email: noreply@example.org
+from_display_name: 事務局
+to: noreply@example.org
+cc: ''
+subject: 一覧」をアップします
+body: 'カテゴリ：全メンバー
+
+  '
+content_type: text/plain
+reply-to: info@example.org
+attachments: []