[CentOS] sendmail sending out on port 587

Gregory P. Ennis PoMec at PoMec.Net
Sun Mar 21 22:47:12 UTC 2010


On Sun, 2010-03-21 at 16:18 -0500, Les Mikesell wrote:
> 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.
> 
Dear Les,


I appreciate your advice about having un-authenticated relaying, and
understand the importance of having this blocked.  My sendmail office
server will only allow relaying with authentication using :

define(`confAUTH_OPTIONS', `A p y')dnl

My problem is using port 587 on the laptop sendmail that is trying to
send e-mail to my office sendmail server.  I have been unable to get
sendmail on the laptop to connect to the office server using port 587.

Your idea of using openvpn is interesting.  I have not experimented with
this yet, but will download it and take a look.  My presumption is that
it needs to be on both the laptop as well as office server.  

If you have other ideas would appreciate your assistance. 

Thanks for your help!!!

Greg



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