# Need workaround to port 25 blocking



## dpalme (Jan 9, 2010)

I do a lot of travel and I hate having to change my mail because of all the port 25 blocking that ISP's are doing; which to me does nothing to prevent spam....but that is another issue.

I want to be able to use my own server (sendmail) all the time regardless.  I recall in days past we had set it up to use a 2525 port and that was a work around, but for the life of me I cannot find those notes.

Any suggestions or links where I can figure out a way to make this work?

Thanks in advance for any assistance.

Douglas


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## phoenix (Jan 9, 2010)

In theory, you should be able to enable port 587, which is the mail submission port (client to mail server), and have it pass through ISP firewalls.  No idea how to do this in sendmail (people still use that?), but I do know that sendmail supports it.  And then configure your e-mail program to use port 587.

Alternatively, you can just do port forwarding on your server, using your packet filter of choice, and have it forward incoming requests to port 25.

Or, you can find out the name/IP of the ISP's mail server, and use that for sending (which is preferred ... everyone should use the local mail server for the network they are connected to).

Or, if your laptop runs a Unix-like system, you can just write a packet filter rule that intercepts outgoing port 25, and forwards it to <wherever>.  That way, you just have to update the rules, and never touch the mail configuration on the laptop.


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## Ruler2112 (Jan 11, 2010)

I do the same thing on my mail server only with a different high port number, but running Postfix.  (No clue how to do it in SendMail - sorry.)  One thing to make sure you do though is ADD the listening on port 2525.  If you replace the listening on port 25 with 2525, you will receive no mail from the outside.

I tried using 587 and was blocked by more than one ISP - some REALLY don't want you sending mail other than with their box!  Another caveat to watch out for is that if you use TLS, Cisco gear with the default configuration will strip the STARTTLS from SMTP conversations on the normal mail ports.


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## danger@ (Jan 11, 2010)

you can tunnel it through ssh - have a look here.


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