SMTP on port other than 25 through DNS???

[Waltner, Steve]

> It's much easier than that... Grab the TIS FWTK (FireWall ToolKit) from
> http://www.tis.com/research/software/ and use the plug-gw software.
> Install this on a friends computer at an ISP that doesn't have port 25
> blocked and setup sendmail on your local sendmail to receive on any port
> besides 25. On the remote system, add the following to
> /usr/local/etc/netperm-table:
> 
> plug-gw: timeout 300 
> plug-gw: port 25 * -plug-to 24.94.1.2 -port 26 
> 
> 24.94.1.2 would be either your IP address or possibly your hostname, and
> the 26 would be whatever port you are running sendmail on. Set your MX
> record to be your friend's IP. The SMTP connection would come into the
> remote system on port 25, and then get relayed to your sendmail system.
> You wouldn't need to manage two sendmail servers since the remote system
> is just relaying the connection to your host. I used in conjunction with a
> SOCKS library to socksify applications that didn't understand SOCKS for
> getting out across our firewall. The connection comes into the internal
> system, gets wrapped with SOCKS and goes out across the Internet to the
> real host.
> 
> I do agree with RoadRunner's decision to block 25. I would guess that
> 99.9% of all SMTP servers setup at someone's home would allow mail
> relaying. This can use incredible amounts of bandwidth.
> 
> -- 
> Steve Waltner 
> LSI Logic 
> Steve.Waltner at lsil.com 
> 
> 	---------- 
> From:   woodside20 at my-deja.com 
> Sent:   Sunday, January 7, 2001 8:30 PM 
> To:     comp-protocols-dns-bind at moderators.isc.org 
> Subject:        Re: SMTP on port other than 25 through DNS??? 
> 
> 	In article <935ajv$1og at pub3.rc.vix.com>, 
>   Barry Margolin <barmar at genuity.net> wrote: 
> > In article <9359ki$1cm at pub3.rc.vix.com>, count0 <tim at timmy.ws> wrote: 
> > > 
> > > 
> > >>I get an IP address through dhcp from roadrunner 
> > >>(cable access).  I also have a second-level domain 
> > >>name resolving to this address through dynamic DNS 
> > >>(nameservers at easydns.com). 
> > >> 
> > >>Problem is that roadrunner blocks port 25 so I 
> > >>can't get any incoming mail. 
> > > 
> > >I though incoming mail was on port 110 (POP3) or IMAP (not sure which 
> > >port) SMTP on port 25 is for sending mail 
> > 
> > He means someone sending mail to his machine using SMTP. 
> > 
> > > 
> > >> I was wondering if I 
> > >>might be able to alter the MX record in the 
> > >>nameserver to specify an alternative port in 
> > >>addition to my hostname, and then I could have my 
> > >>MTA listening in on that port. 
> > 
> > No, there's currently no way to tell all the other mail servers in the 
> > world that you're using a nonstandard port for SMTP service.  This 
> might be 
> > doable in the future with SRV records, but mail systems don't 
> currently 
> > look at them (and since MX records do just about everything that SRV 
> > records do except specifying alternate ports, there's a good chance 
> this 
> > will never change). 
> > 
> 
> 	Would the only option then be to maybe find a friend (who's machine 
> isn't blocked on port 25) who could be a mail relay for me and relay 
> all my mail on a nonstandard port?  I'm assuming that, with prior 
> knowledge, a decent MTA (sendmail, exim, postfix) could be configured 
> to connect on a port other than 25 and avoid my provider's portblock. 
> 
> 	Is this a feasible workaround? 
> 
> 	Thanks for the advice so far and take care, 
> 
> 	Dan 
> 
> 
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> 
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> 
> 
>