Article: https://help.opensrs.com/hc/en-us/articles/203244793-Configure-DNS-for-OpenSRS-Hosted-Email
DNS RECORDS:
mail.example.org. IN CNAME mail.example.org.cust.a.hostedemail.com.
example.org. IN MX 0 mx.example.org.cust.a.hostedemail.com.
SPF Additions:
v=spf1 include:_spf.hostedemail.com ~all
article: https://help.opensrs.com/hc/en-us/articles/203244333-Sender-Policy-Framework-SPF-