ISP blocking port 25 outgoing

My Isp has just started blocking outgoing port 25. I run a small home businness and once a month we send out about 2000 email invoices. I have a colo box that i was connecting to , to send these emails. My ISP also shutsdown its smtp server after i send about 10 emails in arow. I called them and they have acknoloeged  the fact that they block the outgoing.

I can change the port on my smtp server to listen on another port, but my billing program does not allow modifing the port.

So does anyone know how i can do some kind of port forwarding?
if i had a local linux box , i could probably do something.
My router does port forwarding, but only coming in

Any suggestions?

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Netman66Connect With a Mentor Commented:
I'd say you have a business case for what you are doing - why don't you talk with the ISP and arrange something with them that will work.  Perhaps they would be willing to put your server in an exemption list.

I suppose they are trying to either cut down on spam or blocking potential virus activity.

pariesAuthor Commented:
yeah , thier business case it to upgrade to a business cable modem. You get the same speed , the same crappy uptime and all u get is a static ip and unblocked port 25. I do not think that is worth an extra $100/month
Ahh...I didn't realize you were on residential.  You mention a colocated server - what about generating from there?

Sorry took me a long time to find a solution for you... that and I had to go to sleep :)

Download and use this tool.

What you do is redirect your local port 25, to your remote smtp server port ?? (Whatever you set it as).  I have just tested it, my ISP also blocks SMTP.

Command looks something like this:

tcprelay 25 2055

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