At 03:50 PM 13/09/2005, Joseph S D Yao wrote:
Oh, and also ... please consider that some firewalls try to discern whether the connection on port 25 is from a mail server or from Telnet. While I mourn the simplicity of manual debugging of such sites, it remains that: the fact that you can't TELNET HOST.DOMAIN 25 doesn't mean that there's no mail service there.
Making a network connection using the application "telnet" vs the application "sendmail" (or whatever MTA one uses) seems to be the same when doing a tcpdump on the data. I am not sure how a firewall would know -- purely at the network layer -- what the other side's application was/is that initiated the connection. Yes, the other end could try and connect back to the host, but there is no 2 way traffic as the 3way handshake is not completing and I dont see any other traffic coming back from that host attempting to discern any info. ---Mike