Question : Which email does "add to junk senders" add?

It is possible to specify a "From" header when sending email, but the message headers after I receive it show both a Return-Path and a From header.  If I choose "add to junk senders" on that message, which email address does it actually add? The one in the From header, or the Return Path one?

Answer : Which email does "add to junk senders" add?

Return-Path is NOT the field which you can configure in your mail client as a reply-to address.

Return-Path shows which email address was used with the SMTP MAIL FROM command. As the "From" header field is neither mandatory nor 100 % meaningful, Outlook will use the Return-Path field.