An interesting little project just completed. The customer manages upmarket
apartment blocks and provides Internet access via wireless to each apartment.
I have supplied a m0n0-based 'access controller' using the captive portal
with radius to manage access, firewalling and some traffic management.
The customer has a problem with some short-term tenants who need to access
their home ISP mail accounts. The problem is not reading mail, but sending
it. It seems that many ISP's reject relaying from 'foreign' addresses and do
not offer a POP-before-SMTP type solution to allow their users to send email
when on the move.
The solution is quite simple - I modified the captive portal rules
configuration to insert a 'forward' to 127.0.0.1 port 25 for all traffic to
port 25. This then runs to a small CLG that makes a new connection to the
SMTP service of the ISP providing the DSL connection, and then transparently
copies the data between the two TCP connections.
The solution is based around a simple proxy called tcppm that I found in the
If anybody is interested I would be happy to provide the details.
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