I’ve recently been working on a project with a client to introduce emailing of remittences to suppliers. To do this, we switched them from using Outlook foe sending emails to using a shared Exchange mailbox which their IT created for them.
We discovered that while I could use by email address for logging into Exchange, they couldn’t use their shared mailbox. My initial thought was that while we were both using Office365 accounts, they were trying to use an ordinary password, whereas I was using an app password.
I checked that they were entering the credentials correctly, which for Office365 is to use the email address in both the Email Address and Login ID fields (as shown in the example below), and they were: