Hi, until about 3 weeks ago, our domain was sending emails to TPG accounts happily for many years. Now some TPG email users are getting bounce backs with 5.7.23 SPF violation with 5.7.1 SPF unauthorised mail.
Our SPF includes all on prem outbound IP's as well as the usual 365 inclusion. Can anyone shed any light an where to look next? Only TPG email seems to be affected. Thanks.