Issues with mail going to Junk folder on Outlook clients

I'm trying to get rid of our on-prem Exchange 2013 server, to this I've installed the Exchanger 2019 tools on a Windows server. I've re-written our new user script such that it now calls the "Enable-RemoteMailbox" cmd locally instead of opening a PSSession to the Exchange server and running it. The ONLY difference in the script is where it executes the remote mailbox command from.

This is the specific line.

Enable-RemoteMailbox -identity $Alias -RemoteRoutingAddress $Alias"@company.mail.onmicrosoft.com" 

The issue I have is that any user created using the PS tools for Exchange, any mail sent to a Hotmail or outlook.com mailbox will end up in junk folder. Gmail and other O365 recipients are all fine, it only affects outlook.com consumer mailboxes.

I can replicate the same issue just by creating a new user with a mailbox directly in Office365, so I don't think it has anything to do with our hybrid AD config. (I can also replicate this same behaviour in other m365 tenants so this seems like a systemic MS issue)

The mail is all 100% perfect SPF/DKIM/DMARC pass.  As mentioned, the only difference is the way I am invoking the enable-remotemailbox command.

I've had MS Premier support cases open about this before, but they were useless. literally told me to post on public forums for help or talk to the outlook help bot. So here we are.