Getting around ISP SMTP firewall settings (Re: Submitting a new port if send-pr is broken)

Gerard Seibert gerard at
Mon Nov 26 03:17:12 PST 2007

> On November 26, 2007 at 04:00AM Aryeh M. Friedman wrote:

> > You should be able to set up a local mailer/MTA (sendmail, postfix,
> > etc.) and tell it to use your ISP's mail server on TCP port 25, and it
> > all should just "magically work" unless they require SMTP AUTH (not many
> > do from what I've seen; they base authentication on the source IP of
> > customers).
> >
> > sendmail refers to this feature as SMART_HOST, while postfix refers to
> > it as a transport destination (see transport(5)).
> I have not set the MTA up yet for it but I did test it with
> thunderbird... an other question how can I set it up that I can
> receive mail (dynamic IP and 25 inbound is blocked)?

If you attempt to send mail using a dynamic IP, it is going to be blocked by
most MTAs since it fails reverse DNS checking. I am assuming that you are
attempting to bypass your ISP. You have to get a static IP from your provider.
With port 25 presently blocked, you might consider using something like mail
relaying/forwarding from a service like DYNDNS:


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