rDNS: What is reverse DNS ?
Reverse DNS is a way of associating an IP address with its domain name. The reverse DNS identifier is contained in the PTR portion of the IP Zone File. You may look at your reverse DNS using http://dnsstuff.com reverse DNS search tool.
Reverse DNS lookup for your IP address is failing. We does require that all connecting Mail Transfer Agents have established reverse DNS.
If you are on a dynamic IP address, please call your ISP and request a static IP address with proper rDNS before attempting to send mail to us through that server.
If you are on a static IP address, please call your ISP or DNS provider and ask them to establish a reverse DNS record for your IP address, reflecting your correct domain name.
Portscans :
Port scans are an irritation and a possible prelude to hacking attempts from infected machines. Block the following ports as a bare minimum :
Ports to block/Drop inbound /DENY
TCP
1025
135
139
1433
2082
2745
3127
3410
445
5000
5554
6129
UDP
67
137
138
139