Emails are not using the default or custom sender

Emails sent by my task are sent using the email address of the user authenticated to the SMTP service rather than the default sender specified in Email settings or the custom sender specified in my task.

Possible cause  

Your SMTP server authentication does not permit users to override their email address and send emails using another email address.

Proposed action  

Change your SMTP server settings to permit users to override their email addresses and send emails using other email addresses.