I'm running ISPConfig 3.1.13, in the latest Debian 9. Despite me setting up SPF (the TXT record is "v=spf1 mx a ~all" which merely warns on errors), DKIM and DNSSEC the very best I could on my DNS servers, when vacation autoresponses get sent by my ISPconfig-controlled email server, then recipients will get a warning shown as follows: Note: My vacation autoresponses are set up within the ISPConfig Web Admin interface, not from the Roundcube plugin for Vacation autoresponses. I think I know why these Warnings get shown. The headers on outgoing email are a little different for normal outgoing mail, and vacation autoresponses, underlined in red here in this comparison of the headers using "meld": Note that on proper outgoing mail (shown on the left), the header says: "Authenticated Sender:", but in the Vacation Autoresponses (shown on the right), which get flagged, it instead merely says: "from userid 5000". This makes SPF's fur stand on end, as it were. How do I get the vacation autoresponses on the right to have headers just like on the left hand side, saying "Authenticated Sender:"?