Meng Weng Wong wrote:
oh, i just figured out one more class of solutions:
spammers will start to forge www.example.com
receivers will observe that www.example.com has no mx record
receivers will try to connect to port 25
receivers will observe that www.example.com is not an mta
This would not work in following case:
example.com. A 1.2.3.4
example.com. MX 10 mx.example.com.
example.com. TXT "v=spf1 a -all"
mx.example.com. A 1.2.3.4
www.example.com. A 1.2.3.4
Example.com must publish also:
www.example.com. TXT "v=spf1 -all"
Roger