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efg.niemann@googlemail.com (generated from efg@efgn.de) host gmail-smtp-in.l.google.com [142.250.125.27] SMTP error from remote mail server after pipelined end of data: 550-5.7.26 This mail has been blocked because the sender is unauthenticated. 550-5.7.26 Gmail requires all senders to authenticate with either SPF or DKIM. 550-5.7.26 550-5.7.26 Authentication results: 550-5.7.26 DKIM = did not pass 550-5.7.26 SPF [efgn.de] with ip: [80.237.138.238] = did not pass 550-5.7.26 550-5.7.26 To mitigate this issue, please visit Gmail's authentication guide 550-5.7.26 for instructions on setting up authentication: 550 5.7.26 https://support.google.com/mail/answer/81126#authentication g7-20020a05660226c700b0078711abf1c8si3453230ioo.113 - gsmtp