emails with important invoices bounced back as undeliverable to gmail and msn email accounts.

Please help.  We are unable to send emails with important invoices. I have been researching SPF records and attempted to add google and msn to the server to no avail. 

Here was the google message: 

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:

 example@gmail.com
    host gmail-smtp-in.l.google.com [142.250.102.27]
    SMTP error from remote mail server after 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 [raintamerconstruction.co
    550-5.7.26 m] did not pass with ip: [66.96.184.2]. 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. g4-20020a056402180400b00514a5f8d308si816938edy.103 - gsmtp