Emails being marked as spam by microsoft domains only

Hello

We are sending emails from a developed platform via sendgrid. There are 7 'from' addresses all sending from the same platform, so the characteristics are the same on all the emails such as sending IP which is exclusive to us. spf & dkim are fine. 5 of the addresses have a microsoft spam score of 1 and are delivered perfectly to all main clients, however 2 addresses are given a microsoft spam score of 8 and reliably go to junk when being sent to all microsoft domains such as outlook.com or hotmail.com. Out Office365 tenant using MS defender also gives a spam score of 1.

How can i find out why microsoft are giving these 2 email addresses poor spam scores?

Many thanks for any help

Steve