Error
When sending an invoice email, you may see the following error:
EMAIL_ADDRESS_BOUNCED
Root Cause
This error may occur if there was a temporary issue with the recipient's mail server, which caused the email address to be marked as bounced in Salesforce.
Resolution
To remove the bounce alert:
Switch to Salesforce Classic.
Open the affected Contact.
Under the Email Address field, click Confirm Email Address.
Click Save and Remove Bounce Alert.
After that, try sending the invoice email again.
For more information, you can also refer to the Salesforce article.