Wordpress ecommerce integration

I have a wordpress site with ecommerce. The emais sent when something is bought are flagged as spam and/or rejected sometimes because of the spf records. 

How could I add a rule to allow emails sent from my wordpress ?

The error that I keep getting from some domains (governement, schools, hospitals) :

rejected_email  SMTP error from remote mail server after RCPT TO:<rejected_email>:

   host filter1930.zerospam.ca [216.46.2.53]: 550 5.7.1 <rejected_email>:

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

I have read on some forums that I could modify the SPF record :

v=spf1 include:spf.protection.outlook.com a:my-shared-webhosting-dns -all

Thanks !