Troubleshooting Tip: How to resolve when Gmail responds 'Your email has been blocked because the sender is unauthenticated. 550-5.7.26 Gmail requi...pport.google.com/mail/answer/81126'

In the cross-search log, there is this response:

to=, delay=00:00:03(tries=1), xdelay=00:00:03, mailer=esmtp, pri=55998, acl_delivery_id=1, relay=gmail-smtp-in.l.google.com. [x.x.x.x], ip-pool=IP-pool(x.x.x.x), dsn=5.7.26, reply=550-5.7.26 Your email has been blocked because the sender is unauthenticated. 550-5.7.26 Gmail requi...pport.google.com/mail/answer/81126#authentication 41be03b00d2f7-af93b8b732fsi10738617a12.556 - gsmtp, stat=Service unavailable(Reason from remote:550-5.7.26 Your email 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 [domain.local] with ip: [x.x.x.x] = did not pass 550-5.7.26  550-5.7.26  For instructions on setting

This indicates that the protected domain was not properly configured with the necessary SPF, DKIM, and DMARC.

Refer to the below guide to configure the SPF IP and the MX record, etc:
FortiMail Cloud Integration with Microsoft 365 Using MX Records