Add support for extending mail_plugins via extra files

- Modified docker-entrypoint.sh to create empty mail_plugins_extra files
- Updated dovecot.conf to read from additional plugin files
- Added documentation on how to extend mail_plugins

Co-authored-by: DerLinkman <62480600+DerLinkman@users.noreply.github.com>

data/Dockerfiles/dovecot/docker-entrypoint.sh

@@ -121,7 +121,13 @@ echo -n 'quota acl zlib mail_crypt mail_crypt_acl mail_log notify fts fts_flatcu
 echo -n 'quota imap_quota imap_acl acl zlib imap_zlib imap_sieve mail_crypt mail_crypt_acl notify mail_log fts fts_flatcurve listescape replication' > /etc/dovecot/mail_plugins_imap
 echo -n 'quota sieve acl zlib mail_crypt mail_crypt_acl fts fts_flatcurve notify listescape replication' > /etc/dovecot/mail_plugins_lmtp
 fi
-chmod 644 /etc/dovecot/mail_plugins /etc/dovecot/mail_plugins_imap /etc/dovecot/mail_plugins_lmtp /templates/quarantine.tpl
+
+# Create empty extra plugin files if they don't exist (can be populated via extra.conf or direct file)
+[[ ! -f /etc/dovecot/mail_plugins_extra ]] && touch /etc/dovecot/mail_plugins_extra
+[[ ! -f /etc/dovecot/mail_plugins_imap_extra ]] && touch /etc/dovecot/mail_plugins_imap_extra
+[[ ! -f /etc/dovecot/mail_plugins_lmtp_extra ]] && touch /etc/dovecot/mail_plugins_lmtp_extra
+
+chmod 644 /etc/dovecot/mail_plugins /etc/dovecot/mail_plugins_imap /etc/dovecot/mail_plugins_lmtp /etc/dovecot/mail_plugins_extra /etc/dovecot/mail_plugins_imap_extra /etc/dovecot/mail_plugins_lmtp_extra /templates/quarantine.tpl
 
 cat <<EOF > /etc/dovecot/sql/dovecot-dict-sql-userdb.conf
 # Autogenerated by mailcow

data/conf/dovecot/dovecot.conf

@@ -1,6 +1,13 @@
 # --------------------------------------------------------------------------
 # Please create a file "extra.conf" for persistent overrides to dovecot.conf
 # --------------------------------------------------------------------------
+# To extend mail_plugins, you can either:
+# 1. Create/edit /etc/dovecot/mail_plugins_extra (for global plugins)
+# 2. Create/edit /etc/dovecot/mail_plugins_imap_extra (for IMAP-specific plugins)
+# 3. Create/edit /etc/dovecot/mail_plugins_lmtp_extra (for LMTP-specific plugins)
+# For example, to add the virtual plugin globally:
+#   echo -n ' virtual' > data/conf/dovecot/mail_plugins_extra
+# --------------------------------------------------------------------------
 # LDAP example:
 #passdb {
 #  args = /etc/dovecot/ldap/passdb.conf
@@ -21,7 +28,7 @@ disable_plaintext_auth = yes
 login_log_format_elements = "user=<%u> method=%m rip=%r lip=%l mpid=%e %c %k"
 mail_home = /var/vmail/%d/%n
 mail_location = maildir:~/
-mail_plugins = </etc/dovecot/mail_plugins
+mail_plugins = </etc/dovecot/mail_plugins </etc/dovecot/mail_plugins_extra
 mail_attachment_fs = crypt:set_prefix=mail_crypt_global:posix:
 mail_attachment_dir = /var/attachments
 mail_attachment_min_size = 128k
@@ -180,12 +187,12 @@ userdb {
   skip = found
 }
 protocol imap {
-  mail_plugins = </etc/dovecot/mail_plugins_imap
+  mail_plugins = </etc/dovecot/mail_plugins_imap </etc/dovecot/mail_plugins_imap_extra
   imap_metadata = yes
 }
 mail_attribute_dict = file:%h/dovecot-attributes
 protocol lmtp {
-  mail_plugins = </etc/dovecot/mail_plugins_lmtp
+  mail_plugins = </etc/dovecot/mail_plugins_lmtp </etc/dovecot/mail_plugins_lmtp_extra
   auth_socket_path = /var/run/dovecot/auth-master
 }
 protocol sieve {