Re: smtp daemons

[Michael Wood <wood@kingsley.co.za>]

Hi

On Thu, Jun 28, 2001 at 10:00:27PM +0100, Matthew Sackman wrote:
> Hi Guys,
> 
> When you send an email and it goes to the smtp server, that
> server then tries to connect to the mail exchange for the
> domain which the email is going to.
> 
> Will it connect to this mail exchange from port 25, or will it
> open another unpriveledged port? I'm just wondering whether I
> can set a firewall option to only allow connections to the
> smtp server if it comes from port 25.

SMTP clients (including other SMTP servers sending your SMTP
server mail) use an unpriveleged port as the source port.  (I
suppose some clients could use port 25, but I've never seen
that.)

i.e. if you add a rule to allow only tcp src port 25 to tcp dst
port 25, you will not get mail.

-- 
Michael Wood        | Tel: +27 21 762 0276 | http://www.kingsley.co.za/
wood@kingsley.co.za | Fax: +27 21 761 9930 | Kingsley Technologies