Not Receiving Password Reset Email for Free Tier OCI Account

Question
Why are sign-up and password reset emails not being delivered to Hotmail accounts in Oracle Cloud Free Tier tenancies, while the same Hotmail accounts work in paid OCI accounts?

Summary
We created Oracle Cloud Free Tier accounts for testing and found that users with Hotmail email addresses do not receive sign-up emails or password reset emails. Users with other email providers receive these emails without issue.

We tested the same Hotmail accounts in a paid OCI account, and email delivery works there. We also repeated the test across multiple Free Tier tenancies and multiple different Hotmail accounts, with the same result each time.