As long term Outlook.com user all I can say it's their service is extremely unreliable, my emails are either not delivered at all or end up in junk mail, some emails I don't receive at all or my partners are rate limited sometimes receiving their emails with hours long delays.

I assume also their junk filters block some emails and there is no way to avoid it, you repeatedly add senders to safe senders list, even to safe subscriptions and their email still end up marked as junk even after years long communication from same addresses.

As backup when something important I write email to recipient from gmail whether they received my email from outlook only to find out my email was never received.