Need to get un-blacklisted by Microsoft

Starting about a month ago, probably due to some security upgrades by Microsoft, my emails to Hotmail, Outlook, and any .msn address are being bounced. I've spent hours getting nowhere on this. Need someone with experience on this blacklisting issue. You should know that:

1. I have a blog that sends out a couple hundred email notifications every Monday. Other email traffic is normal. No ideas why I got blacklisted. Nothing on my end has changed.
2. BlueHost, my email server, tells me there has been no suspicious email activity in any of my email accounts. I also have the required SPF on my domain.
3. I'm prepared to send whatever creds are required to resolve this, but really require someone with experience in these matters.
4. I've been working with tech for decades, and I usually solve my own problems, but this one has me stumped. I expect my hire to communicate clearly exactly what they did to resolve this email issue. I need to learn.