Re: Tunneling smtp with exim4

[Christoph Sticksel <spamwonderfulspam@gmx.net>]

> I normally use exim4 with the "smarthost-configuration", i.e. I relay all
> email to the mail server of my ISP. In the file
> /etc/exim4/update-exim4.conf.conf i thus have a line saying:
> 
> dc_smarthost='mail.my.isp.se'
> 
> Now I would like to tunnel my outgoing email over ssh, and I have started
> up an ssh tunnel with:
> 
> ssh -l jesper -L 1369:mail.my.isp.se:25 -N shell.my.isp.se
 
I had the same problem reaching a relaying mail server through a tunnel. I
found http://www.jfranken.de/homepages/johannes/vortraege/ssh2.en.html. The
solution is to make exim talk smtp to a pipe. ssh takes this smtp dialog on
stdin and netcat on the remote machine feeds that to the mail server.

In the transports section I put:

# Transport, which tunnels mails over ssh to my smarthost
ssh:
  driver = pipe

  # talk regular smtp to the pipe (qmail approved :-) )
  bsmtp = all
  bsmtp_helo = true
  use_crlf = true
  prefix = ""
  suffix = ""

# connect to my mail server's smtp port.
# must authenticate without password
  command = ssh -l <user> <host> 'nc -w 1 <smtp server> smtp'
  user = <local user>

# ssh failure handling: kill hanging sessions,
# retry and tell me on failures
  timeout = 300s
  temp_errors = 1
  return_fail_output = true


And in the routers section there is 

sshpipe:
  driver = domainlist
  transport = ssh
  route_list = "*"

Important to note is that you need to enable ssh's public key authentication
to not have it ask for a password. Key authentication has to work for 
user = <local user> in the line after the ssh command.

BTW, I use exin 3.36, I believe this has to work with other versions, too.
No experiences there, sorry

HTH,
Chris