Hello
Can you use the instruction here to bring up the email header/source: https://support.microsoft.com/en-us/office/view-internet-message-headers-in-outlook-cd039382-dc6e-4264-ac74-c048563d212c#tab=web
Then share what the source says. Please edit to remove your personal information, such as your email address.
The source file would provide an idea why it was identified as junk/spam.