adding additional sendmail process?

[Chris Yuzik]

Terry Hope wrote:

>The ISP at the client side is blocking outgoing port 25 - the mail server is
>NOT handled by this ISP - so the real problem is sending e-mail via my
>corporate e-mail account while I am on my home ISP.
>I can send mail via the corporate mail server when I am at a client
>company's site that does not block outbound port 25. So I just need to be
>able to send out - preferably without needing any sort of tunneling (this is
>just a single example of the issue - I have to support multiple users with
>the same issue from other ISPs in the area) from the ISP that blocks port
>25.
>Changing ISPs is not an option - nor is providing dial-up or VPN access at
>the corporate side.
>
>
Terry,

I've seen this before as well. One of my users is a part-time
road-warrior, and uses dial-up while travelling. His dial-up IP requires
him to use their smtp server and blocks all outbound traffic on port 25.
But this is a hassle because it means he has to change every email
account he has, ever time he goes on a trip and when he returns.

Adding another sendmail process isn't the answer, imo, and is probably
much more complex than it's worth.

Simple solution: set your server to listed on port 25 AND another port
by using iptables.

Try this (works on Redhat):
iptables -t nat -A PREROUTING -p tcp -d 11.22.33.44 --dport 30 -j DNAT
--to 11.22.33.44:25

Obviously, substitute the IP address of your server for "11.22.33.44".
You don't have to use port 30, as in "--dport 30" above, you could use
any unused port.

Let me know if this works for you.

Cheers,
Chris