Our client is using GP18.5. On workflows, the reminder and escalation emails are not sent to the approvers. This is disappointing to the client as they expect this feature to work. After extensive research and testing, we have found that when you do something with workflow and emailing in the front-end of GP, it uses Modern Authentication; however, the reminder and escalation notifications come from the SQL Agent jobs that use SMTP.

The SMTP isn't working anymore, most likely because it is being deprecated by the Exchange Online team, as mentioned in the blog posts that I have read and been provided by support.

What is concerning is that I would have thought that since Basic authentication is being deprecated, reminder and escalation emails should be using Modern Auth as the front end is when the first email is sent out advising the approvers they have a batch to approve in the workflow.