cannot send email to gmail accounts

I cannot send email to gmail accounts.  I keep getting a mail system delivery failure message followed by:

host gmail-smtp-in.l.google.com [74.125.136.26]

    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 [empirerealestateschool.com] with ip:

    [66.96.185.4] = did not

    550-5.7.26 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 y6-20020a25ad06000000b00d78336e6470si3277405ybi.102 - gsmtp

Please advise how to fix this problem.