On April 2^nd, 2025 Microsoft announced new bulk sender requirements that apply to hotmail.com, live.com and outlook.com.

Basically these are similar to Google's bulk sender requirements by making mandatory SPF, DKIM, DMARC settings.

In addition senders must conform to some standard, basic good practices such as valid "From" and "Reply-to" addresses, functional opt-out links and low bounces and complaints rates.

You can read the complete announcement with all details here.