Users do not receive the B2C verification code email

Question

Hello!

We are currently facing an issue where some users trying to log in to a B2C tenant app, but not getting their email verification code in their inbox.

I confirmed with users that the emails didn't reach their Spam folders either.

Azure B2C is used for user management in the system.

The following domains seem to have issues: @loopingone.com.

Before today, emails were received successfully for the above domain.

For other domains it's working fine and emails are received.

The email subj and sender are like this:

From: ****@microsoftonline.com

Subject: <Tenant name> account email verification code

Tell me please is there any way to resolve this issue?

And are there any ways to get the logs for this operation and see why the emails were not sent by Microsoft to those particular recipients ?