An SPF record can help you authorize your authentic sending source. Here for example, if you are using JustHost to relay emails on your behalf, you need to set up the protocol for JustHost. You can do so by following these steps: 

Creating an SPF record on JustHost

Here are the steps to set up SPF for JustHost :

• Login to your DNS management console 
• Navigate to Tools & Settings > DNS Template
• You need to edit the DNS TXT record related to SPF
• An SPF TXT record for JustHost will have the following syntax: 

mydomain.com    TXT  v=spf1 include:justhost.com -all

• Publish this record in your DNS records section for your respective domain.

Note: If you don’t have an SPF record previously for your domain, simply publish the above-mentioned record to enable SPF for outgoing emails using JustHost. If you do have an existing SPF record in your DNS, you need to modify it to include JustHost, as shown below:

Previous SPF record:  v=spf1 a mx -all

Modified SPF record:  v=spf1 a mx include:justhost.com -all

• Save changes 
• Wait for 72 hours to allow your DNS to process the changes  

Finally, you can look up your record using our SPF record lookup tool, and enable DMARC for your domains: take a DMARC trial.