Restore detailed backup mail reports with bounded local delivery

etc/app-backup/app-backup.conf

@@ -38,6 +38,12 @@ RCLONE_ONEDRIVE_CHUNK_SIZE="80Mi"
 RCLONE_BWLIMIT="0"
 ENABLE_MAIL_REPORT="true"
 MAIL_TO="johannes"
+# Empty means app-backup@<FQDN>. Existing sender/subject/tail settings are preserved.
+MAIL_FROM=""
+MAIL_SUBJECT_PREFIX="[app-backup]"
+MAIL_INCLUDE_LOG_TAIL_LINES=200
+MAIL_SENDMAIL_BIN="/usr/sbin/sendmail"
+MAIL_SEND_TIMEOUT=30
 
 ENABLE_WORDPRESS="true"
 WP_DIR="/var/www/html"