emails to GMAil rejected

Please advise what to do

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:

 

  margaret.crosby6@gmail.com

    host gmail-smtp-in.l.google.com [142.250.102.26]

    SMTP error from remote mail server after pipelined end of data:

    550-5.7.26 This mail is unauthenticated, which poses a security risk to the

    550-5.7.26 sender and Gmail users, and has been blocked. The sender must

    550-5.7.26 authenticate with at least one of SPF or DKIM. For this message,

    550-5.7.26 DKIM checks did not pass and SPF check for [paceltd.com] did not

    550-5.7.26 pass with ip: [66.96.188.9]. The sender should visit

    550-5.7.26  https://support.google.com/mail/answer/81126#authentication for

    550 5.7.26 instructions on setting up authentication. we8-20020a170907234800b0096f8bd93da6si1272732ejb.1007 - gsmtp