550 SPF Sender Invalid


I’m hosting a client’s site at Dreamhost, including their email, and suddenly their emails to any other email hosted on an Office 365 server is getting rejected with this error: 550 SPF Sender Invalid - envelope rejected. I’ve tried everything I can find regarding SPF and DMARC records, but the problem persists. Any suggestions?


What’s the SPF record for the site? Maybe it is declaring the wrong outgoing servers, etc.