Using Classic Outlook on Windows for personal email, calendar, and contact management
Hello Donna, I just reviewed this sender's public domain records, specifically for SPF, DKIM and DMARC records, they were not set up at all. That's the reason Microsoft reject their emails.
Microsoft is now requiring business senders, especially high volumn senders to set up these three records. These records basically proved that they are who they say they are, since email spoofing is a real threat nowadays. If these records are not set up, Microsoft cannot verify that they are truly sent by LakeCityTravel.com and can be spoofed, hence it was rejected.
Unfortunately only domain owner can access their DNS records to add these three records, Once added, their emails should be accepted again. Sorry, this is not something you can fix on their end.