[StAPF] Undelivered Mail Returned to Sender

This is the mail system at host forward-relay.netcup.net. I'm sorry to have to inform you that your message could not be delivered to one or more recipients. It's attached below. For further assistance, please send mail to postmaster. If you do so, please include this problem report. You can delete your own text from the attached returned message. The mail system <fs.sprachkultur(a)gmail.com&gt;: host gmail-smtp-in.l.google.com[2a00:1450:4013:c1a::1b] said: 550-5.7.26 The MAIL FROM domain [zapf.in] has an SPF record with a hard fail 550-5.7.26 policy (-all) but it fails to pass SPF checks with the ip: 550-5.7.26 [2a03:4000:21:611:1479:86ff:fe4e:c332]. To best protect our users 550-5.7.26 from spam and phishing, the message has been blocked. For 550-5.7.26 instructions on setting up authentication, go to 550 5.7.26 https://support.google.com/mail/answer/81126#authentication s3-20020a170906354300b00a23b4407b54si3024072eja.346 - gsmtp (in reply to end of DATA command)