Sender Policy Framework (SPF) is an open standard to prevent sender address forgery. An SPF record is a type of Domain Name Service (DNS) record that identifies which mail servers are permitted to send email messages on behalf of your domain. The purpose of an SPF record is to prevent spammers from sending messages with forged addresses at your domain.
If you have an SPF record for your domain, add required values to the current record for Trend Micro. For example, change the following TXT record:
v=spf1 ip4:x.x.x.x include:spf.example.com ~all
v=spf1 ip4:x.x.x.x include:SPF record under the Outbound Server section include:spf.example.com ~all
A domain cannot have more than one TXT record for SPF. If your domain has more than one SPF record, a message delivery or spam classification issue may occur.