Setting Your SPF Record
1. Log in to the administrative console for your domain.
2. Locate the page from which you can update the DNS records. You may need to enable advanced settings.
3. Create a TXT (if one doesn't already exist) record containing this text:
v=spf1 include:mailSPF.smtp.com ?all
4. If a TXT record already exists (that starts with v=spf) then you want to modify it to include the following:
If you have this:
v=spf1 a mx ptr include:bluehost.com ?all
You'll want to change it to this:
v=spf1 a mx ptr include:bluehost.com include:mailSPF.smtp.com ?all
When you are finished, you can use any SPF record checker online such as the following one to make sure you have it properly set.
Here's some set up guides for commonly used domains: