Set up SPF
SPF (Sender Policy Framework) is used to restrict which mail servers are allowed to send email for your domain name. This framework is designed to detect and block email spoofing by providing a mechanism to allow receiving mail exchangers to verify that incoming mail from a domain comes from an IP Address authorized by that domain's administrators. The list of authorized sending hosts and IP addresses for a domain is published in the DNS records in the form of an SPF record which is a specially formatted TEXT record.
An example of an SPF would be : example.com. TXT "v=spf1 -all"
Forwarding emails can sometimes break the SPF. If this is the case we recommend using SRS (Sender Rewriting Scheme - http://www.openspf.org/SRS).
Hosted Cloud Users
For details, see Set up Your SMTP Hostname.
Local Cloud Users
We recommend you create a similar DNS hostname as above, however for SPF we would recommend to add all cluster IP's to the hostname, so that if IPs are changed/rotated, no changes are needed to be made to senders SPF records.
spf.example.tld > A > Primary IP 1st server
spf.example.tld > A > Secondary IP 1st server
spf.example.tld > A > Tertiary IP 1st server
spf.example.tld > A > Primary IP 2nd server
spf.example.tld > A > Secondary IP 2nd server
spf.example.tld > A > Tertiary IP 2nd server
If your sending domains already use SPF, then you simply need to add "a:spf.example.tld" to their existing TXT record. If they do not have a SPF record, and you wish to configure this, (and restrict all email to the Spam Experts server), then you can create something like this: "v=spf1 a:spf.hostname.tld -all"