Email Issues - Again. Please Help :(

hello to all of you.

I have been experiencing lots of bounced back email from places. I have had issues where they are blocking my domain and email and also issues where I get this error.

Recipient address rejected: Message rejected due to: SPF fail - not authorized

I have my text set and my SPF turned on, I am just at aw because I cannot figure out what I need to do. Here are mt setting for the email.

SETTINGS
Installed mail server QMail
Installed IMAP/POP3 server Dovecot

SPF turned on...

Email Issues - Again. Please Help