mail server DNS configuration questions

CyberLeo Kitsana cyberleo at
Thu Sep 11 21:18:12 UTC 2008

Andrew Falanga wrote:
> ...
> While diagnosing this, I connect to the server (using Putty) from a
> machine in PN1, using either a mail client or telnet I'm unable to make
> a connection to the mail server over port 25.  Using tcpdump during this
> putty session I do not even see the SYN packets for the start of the
> connection from the machines in PN1.  This is only when connecting to
> port 25.  Obviously, I can connect to the server because I'm using
> ...

Are you sure CableOne does not filter outgoing port 25 connection
attempts to any servers save it's own relay?

My ISP (A big name DSL provider; grep the headers if curious) does not
perform incoming port filtering, but rather aggressively filters
outbound TCP port 25 and (for reasons unexplained) 4444 as well.

Fuzzy love,
Technical Administrator
CyberLeo.Net Webhosting
<CyberLeo at CyberLeo.Net>

Furry Peace! -

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