[2024-feb-29] Sad news: Eric Layton aka Nocturnal Slacker aka vtel57 passed away on Feb 26th, shortly after hospitalization. He was one of our Wiki's most prominent admins. He will be missed.
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howtos:misc:proxying_smpt [2015/11/27 23:27 (UTC)] – [Scenario 2] louigi600 | proxying_smtp [2016/06/20 07:21 (UTC)] – howtos:misc:proxying_smpt renamed to proxying_smtp (Typo in the page name) alienbob | ||
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Here are some scenarios with examples on how you could go about working around the problem. | Here are some scenarios with examples on how you could go about working around the problem. | ||
- | Throughout the scenarios we will be referring | + | Throughout the scenarios we will be referring |
- | * Machine A with IP address 192.168.0.2 (cannot send meils directly via internet and cannot | + | * Machine A with IP address 192.168.0.2 (cannot send mails directly via internet and cannot |
* Machine B with IP address 192.168.1.2 | * Machine B with IP address 192.168.1.2 | ||
* Local Mail Relay (LMR) with IP address 192.168.2.2 | * Local Mail Relay (LMR) with IP address 192.168.2.2 | ||
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===== Scenario 1 ===== | ===== Scenario 1 ===== | ||
- | Machine A cannot | + | * Machine A cannot |
- | but Machine A has access to machine | + | |
+ | * Machine B can relay thought LMR | ||
+ | * Machine B can reach LMR's port 25 | ||
- | We can use nc to proxy mail from A to LMR | + | We can use nc on Machine B to proxy mail from A to LMR. In this example it will appear to LMR as if it was Machine B that is sending the email. |
On machine B | On machine B | ||
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* Machine A can reach the LMR but only on port 22. | * Machine A can reach the LMR but only on port 22. | ||
- | We use a ssh tunnel between A and LMR to do the job for us. | + | We use a ssh tunnel between A and LMR to do the job for us. In this example we are bypassing firewall by using ssh to forward traffic trough a encrypted tunnel. For this to work properly the ssh client that is going to be forwarding needs to be executed by an administrative account. |
<note important> | <note important> | ||
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DATA | DATA | ||
354 End data with < | 354 End data with < | ||
- | FROM:drao@invallee.it | + | FROM:me@localnet.com |
- | TO:drao@invallee.it | + | TO:dude@localnet.com |
SUBJECT: | SUBJECT: | ||
if you get this sending email trough ssh tunnel worked | if you get this sending email trough ssh tunnel worked | ||
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We can then start the ssh socks proxy on Machine B listening on a port Machine A can access: | We can then start the ssh socks proxy on Machine B listening on a port Machine A can access: | ||
- | On machine B | + | On machine B with a privileged user |
ssh -2 -D 192.168.1.2: | ssh -2 -D 192.168.1.2: | ||
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DATA | DATA | ||
354 End data with < | 354 End data with < | ||
- | FROM:drao@invallee.it | + | FROM:me@localnet.com |
- | TO:drao@invallee.it | + | TO:dude@localnet.com |
SUBJECT: | SUBJECT: | ||
if you get this sending email trough ssh tunnel worked | if you get this sending email trough ssh tunnel worked | ||
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===== Scenario 4 ===== | ===== Scenario 4 ===== | ||
- | Mostly like Scenario 2 but Machine A is not allowed to relay on LMR dew to MTA configuration. | + | * Machine A cannot reach LMR's port 25 |
+ | * Machine A is not allowed to relay thought | ||
+ | * Machine A cannot proxy on any other machine that is allowed | ||
+ | * Machine A can reach the LMR but only on port 22. | ||
We can still get the whole command to run on the LMR via ssh: | We can still get the whole command to run on the LMR via ssh: | ||
+ | |||
+ | <note important> | ||
cat << EOF > send_this_mail | cat << EOF > send_this_mail | ||
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====== NOTES ====== | ====== NOTES ====== | ||
- | The command we used above is probably a good example of bad unixcraft, let me give a brief explanation on how it works. | + | The command we used in Scenario 1 is probably a good example of bad unixcraft, let me give a brief explanation on how it works. |
Let's momentarely get rid of the odd use of the fifo by just using this: | Let's momentarely get rid of the odd use of the fifo by just using this: | ||
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so now the whole command line looks like this: | so now the whole command line looks like this: | ||
cat /tmp/f | nc -l -p 1234 -s 192.168.1.2 | nc 192.168.2.2 25 >> /tmp/f | cat /tmp/f | nc -l -p 1234 -s 192.168.1.2 | nc 192.168.2.2 25 >> /tmp/f | ||
- | it is possible to do the same thing without having to use cat it is a little neater but still bad unixcraft | + | it is possible to do the same thing without having to use cat, it is a little neater but still bad unixcraft |
nc -l -p 1234 -s 192.168.1.2 < /tmp/f |nc 192.168.2.2 25 >> /tmp/f | nc -l -p 1234 -s 192.168.1.2 < /tmp/f |nc 192.168.2.2 25 >> /tmp/f | ||