Depending on your site's email notification usage, you will want to consider either the standard mail service, or a mail relay service. 

STANDARD MAILBOX SERVICE

• For use by sites with lower sending requirements - on average, less than 9,000 emails per day - please confirm with your email service provider for exact limits. 
• It is advised to set up your SMTP with a third-party authentication password instead of a regular mailbox. This will help to ensure emails are sent and not flagged as spam. 
• Read Microsoft's Learning Information on how to manage this here: Option 1: Authenticate your device or application directly with a Microsoft 365 or Office 365 mailbox, and send mail using SMTP AUTH client submission
• Organizations should not use standard mailbox accounts for bulk or high-volume outbound emails (over 10,000 emails per day).

MAIL RELAY SERVICE 

• Using a mail relay service for your website’s email notifications ensures reliable and secure delivery of your emails.
• The service handles the sending infrastructure, manages large volumes of emails efficiently, helps prevent your messages from being marked as spam, and protects your sender reputation by authenticating and encrypting outgoing emails. This means your notifications reach your recipients consistently while reducing the risk of delivery failures or blacklisting.
• Here is the official Microsoft 365 help article on how to set up your multifunction device or application to send email using Microsoft 365 or Office 365 SMTP relay: 
  • How to set up a multifunction device or application to send email using Microsoft 365 or Office 365
  • This guide covers the requirements for SMTP relay, connector configuration, and detailed steps to ensure your emails from your website or application are properly sent and authenticated via Microsoft 365.

Once you have your settings available, please enter them as outlined on Change to own SMTP mail service