If you did not reach the 3 domain limit, you can add a new one, make it the default domain, and then delete the old one. After the old one is deleted, readd it, reset it as default, and delete the temporarily added one.
https://gjr.x10.mx/#mail
Port 587
STARTTLS encryption
User name would be the full noreply@mydomain.com
Password would be the password you configured for that account when you created it.
On the new domain, is SPF configured properly? is DKIM enabled? Is a DMARC record present? If at least one of these are missing or not configured correctly, can lead to other mail servers rejecting the message outright.
You would have to contact MS for this. The MX record for your domain is pointing to them.
MX record for your domain points to onlinegruposabemas-x10-bz.mail.protection.outlook.com which means Microsoft is hosting emails for your domain based on your configuration.