SPF (Sender Policy Framework) is a kind of DNS record, in order to fight spam and increase the deliverability of your email messages.
It's a TXT record, which specify a list of authorized SMTP servers which are allowed to send messages for your domain.
SMTP servers can be specified with their hostnames or (much better) by IP number.
Syntax of SPF records is not simple; a SPF simple record is something like this:
v=spf1 mx a ip4:184.108.40.206 -all
but there're a number of free tools and resources to help you:
SPF Record Syntax: http://www.openspf.org/SPF_Record_Syntax
SPF Wizard: http://www.spfwizard.net/
Common mistakes when creating a SPF record: http://www.openspf.org/FAQ/Common_mistakes
SPF Record testing Tools: http://www.kitterman.com/spf/validate.html
Confused? Let us do it for you!
Compiling an SPF record may be really complex and subject to hardly recognizable errors, but which may affect the deliveryability of your email service.
About this matter, we can assist you and provide you with a very cost effective consulting service.
If necessary, raise a ticket in your client area.