If Blackbaud SSO is set up using Azure ADFS, Azure may be returning the user's primary SMTP email address, which may not match their Blackbaud ID username email address. For example, Azure may be returning john.smith@savethepuppies.onmicrosoft.com instead of john.smith@savethepuppies.org.

You'll want to review the user's account in Azure. You may need to update their SMTP email address to match the email address configured as their Blackbaud ID username.