Lookup SMTP Hosts in DNS The 'Lookup SMTP hosts in DNS' option located within the MailSite SMTP security or Anti Spam menu carries out a reverse lookup on the IP of any incoming host. This feature only checks for the existence of a reverse record and does NOT carry out any forward verification on that record. For example: Incoming connection from intmail.anycompany.com which has the IP 11.22.33.44 is queried for a PTR record and response received is 11.22.33.44 = mail.anycompany.com. This connection will be accepted, since there is a PTR present for the IP address.