I'm using a dedicated server from Hetzner in Germany with ISPConfig and Ubuntu 16.04. This server manages our web-domains and mail-domains and has it's own RDNS mail.example.com. Other domains on this server are 123.de, 456.de, 789.de. MX-, A- and TXT-Records are managed by myself, but external over my Registrar-Accounts (HostEurope and Schlundtech). For each mail-domain I'm using DKIM and DMARC and created individual A-, MX- and TXT-Records as there are (short version): 123.de A IPv4 123.de TXT "v=spf1 a mx ~all" 123.de MX 10 mail.123.de However, If I'm using some Formmailer on that server, the Mailheader might show up with [email protected]. So, to be safe, should I include the RDNS mail.example.com in my SPF-Record: "v=spf1 a mx a:mail.example.com ~all" ? Reason: At the moment gmx and web.de in germany are a pain in the ass and I'm trying to figure out, why our mails get permanently blocked without being on any RBL-List. mxtoolbox tells me everything is fine, but maybe the Formmailer, sending out copies to our customers by using the Server-RDNS, is - not being included in my SPF - a kind of reason?