Email reminder sent using the Reminder Sender Job are sent using the practice Mail Server settings, but the From address is determined by the customer's Practice Location.
This causes problems with SMTP servers that require the username and address to be the same.
E.g. outlook.com reports the following:
When sending reminder emails, the Mail Server associated with the customer's Practice Location should be used, and the From Address should come from that Practice Location. If there is no Mail Server or contact associated with the Practice Location, then the Practice settings should be used.