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 -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 ?all