Cannot "send mail as" using gmail. It shows these errors

Cannot "send mail as" using gmail. It shows these errors

ERROR CODE :550 - 5.7.26 Unauthenticated email from gmail.com is not accepted due to domain's
            5.7.26 DMARC policy. Please contact the administrator of gmail.com domain
            5.7.26 if this was a legitimate mail. To learn about the DMARC initiative,
            5.7.26 go to
            5.7.26 https://support.google.com/mail/?p=DmarcRejection 41be03b00d2f7-7a9f69dd7c4si17155745a12.245 - gsmtp