[CentOS] sendmail sending out on port 587

Les Mikesell lesmikesell at gmail.com
Sun Mar 21 22:18:51 UTC 2010


Gregory P. Ennis wrote:
> Dear List,
> 
> I recently spent some time out of the USA, and found myself in a hotel
> that blocked port 25 which prevented my laptop's ability to connect to
> my office mail server.  I did a scan on the internet and made the
> observation that this was a common problem.  I had port 22 available so
> I was able to get my office server set up to accept mail on 25 and 587
> without difficulty.  The command "telnet mail.server.com 587" to my
> office mail server connects without difficulty.  
> 
> However, I have not been able to get sendmail on my laptop to connect to
> sendmail on my mail server at home using port 587.  
> 
> I have added the following to sendmail.mc on my laptop without success :
> 
> define(`RELAY_MAILER_ARGS', `TCP $h 587')
> define(`ESMTP_MAILER_ARGS', `TCP $h 587')
> 
> I finally made it back home, but have decided to change my configuration
> to use 587 by default so that this problem will be avoided, but I have
> been unable to get my laptop to connect.   
> 
> Anyone having ideas would be appreciated.

Usually you would block 587 inbound on your own office firewall and use that to 
distinguish between locally-submitted mail and internet-received.  You 
definitely don't want to permit relaying from un-authenticated internet sources. 
   If you need access to other office resources, one approach would be to set up 
openvpn on an office server and the laptop so you have an encrypted connection 
through the firewall.  Another would be to set up sendmail to require 
authentication on port 587 and also set up your laptop to send authentication.

-- 
   Les Mikesell
    lesmikesell at gmail.com



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