I’ve run a VPS for some years - running Postfix and last year noticed a couple of bounce backs from MS, refusing delivery of emails. No mail accounts were spamming.
Joined Microsoft’s SNDS - Smart Network Data Service & Junk Mail Reporting Program, both free. You do need an hotmail account to join\register.
Allows you to keep an eye on the status of your VPS IP addresses and to receive copies of emails marked\identified as spam by recipients.
Thought it might be useful to folks.