You would add the below TXT record to your DNS to prevent the email spoof error if you did not purchase a custom URL.

TXT     @     v=spf1 mx a a:dedrelay.secureserver.net -all


Note that you can only have one SPF record in a DNS file, so if you already have one, you need to combine them.

For example:

combining mail chimp and grow labs SPF into one SPF

v=spf1 include:servers.mcsv.net include:mailgun.org include:spf.mailjet.com include:servers.mcsv.net ?all