This message was created automatically by mail delivery software. A message that you sent could not be delivered to one or more of its recipients. This is a permanent error. The following address(es) failed: muyiwacaleb@gmail.com host gmail-smtp-in.l.google.com [142.251.31.27] SMTP error from remote mail server after pipelined end of data: 550-5.7.26 Your email 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 [www529.your-server.de] with ip: [188.40.30.73] = did not pass 550-5.7.26 550-5.7.26 For instructions on setting up authentication, go to 550 5.7.26 https://support.google.com/mail/answer/81126#authentication a640c23a62f3a-aab9635ef14si351285166b.793 - gsmtp