So we need to find and alternative. Yes you can setup your own in house SMTP server but that takes time and then you have to monitor it to make sure it is running. We at Jarvie Computing use a SMTP server: 18.104.22.168 which requires no authentication.
We only use it to send server or network issues and reports. If we use nslookup to resolve IP address to host-name you will see that it is provided by Microsoft.
Jarvie Computing provide email and collaboration solutions to small business.