smtp; 550 5.0.0 This mail has been blocked because the sender is unauthenticated. Gmail requires all senders to authenticate with either SPF or DKIM. Authentication results: DKIM = did not pass SPF [itzmx.com] with ip: [103.129.255.227] = did not pass To mitigate this issue, please visit Gmail's authentication guide for instructions on setting up authentication: https://support.google.com/mail/answer/81126#authentication - gsmtp(in reply to end of DATA command)