SPF issue: what causes softfail?

Question

Whenever I use PHP to send emails to members of my site, the email ends up in the spam folder for most email providers like Gmail and Hotmail.

When I check the original

Answer 1

The Return-Path header is empty. This means that during the SMTP conversation, the MAIL FROM command did not specify an email address where bounces are sent. It is the domain from this email address that SPF tests. If there is no email address, a softfail will result.