Mention how to migrate DKIM keys.

convert.sh

@@ -22,7 +22,7 @@ strip_name_prefix()
 }
 
 # Available translations
-all_languages='en_US zh_CN'
+all_languages='en_US'
 
 # Chapter directories in specified order
 all_chapter_dirs="overview \
@@ -45,7 +45,7 @@ article_counter=0
 echo -n "* Processing Markdown files: "
 
 for lang in ${all_languages}; do
-    src_dir="${ROOTDIR}/docs/${lang}"
+    src_dir="${ROOTDIR}/${lang}"
     if [ ! -d ${src_dir} ]; then
         echo "* [SKIP] No translation for ${lang} (${src_dir})."
         break

en_US/migrations/migrate.to.new.iredmail.server.md

@@ -136,3 +136,13 @@ $ ldapsearch -x -D 'cn=Manager,dc=xx,dc=xx' -b 'o=domains,dc=xx,dc=xx' -W "(mail
 
 * Export/import roundcube webmail database, and upgrade database to work with new version of Roundcube.
 <http://trac.roundcube.net/wiki/Howto_Upgrade>
+
+## Migrate DKIM keys
+
+Amavisd will read DKIM keys and sign outgoing emails. DKIM keys are stored
+under `/var/lib/dkim` by default, you can copy all keys under this directory to
+new server, and make sure they have correct file owner `amavis:amavis` and
+permission `0600`.
+
+If you prefer generating new DKIM keys on new server, don't forget to update
+DNS records for mail domain names.