When your visitor submits the form or registers on your website, it will have an email sent directly to all visitors/members. But some of an email go to recipient's junk box. To prevent this issue, please inform your hosting provider to check with the following list.
1. Changing Mail Server to SMTP (Simple Mail Transfer Protocol)
The default setting is sendmail which is not reliable, we suggest to use an SMTP instead.
2. Checking SPF (Sender Policy Framework) and DKIM (Domain Keys Identified Mail) Record
SPF allows the receiving mail server to check during mail delivery that a mail claiming to come from a specific domain is submitted by 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 for that domain.
DKIM (Domain Keys Identified Mail) is a method to validate the authenticity of email messages. When each email is sent, it is signed using a private key and then validated on the receiving mail server (or ISP) using a public key that is in DNS.
3. Checking PTR (POINTER) Record
PTR records provide trust that the given hostname or a domain are connected to the IP address. The PTR records are must-have for outgoing mail servers because most of the mail providers reject or mark as spam messages received by mail servers without valid reverse DNS configuration (missing PTR or mismatch A record for the hostname).