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Re: Simple Linux to Linux(Debian) email

You might check out sSMTP[1]

[1] https://wiki.debian.org/sSMTP

On Mon, Apr 08, 2019 at 09:33:03PM +0900, Mark Fletcher wrote:
> Hello all
> As I wrote this I began to consider this is slightly OT for this list; 
> my apologies for not putting OT in the subject line but mutt won't let 
> me go back and edit the subject line.
> Short version: Is it reasonable to expect a piece of software to exist 
> that establishes a direct connection to a "remote" MTA and delivers mail 
> there for delivery, without also offering up mail reception 
> capabilities? If it is, what would that software be? Or alternatively, 
> is there a failsafe way to configure one of the MTAs (I have no strong 
> allegiance to any MTA, although the only one I have experience with is 
> exim4) such that even if I miss a configuration step it won't be 
> contactable from outside? To be clear, I only wish to be able to send 
> mail in one direction in this scenario...
> The more detailed background:
> My ISP has recently developed the unfortunate habit of changing my IP 
> address moderately frequently. They're allowed -- I'm cheap so I haven't 
> paid for a fixed IP. I'm shortly going to be moving so now really isn't 
> a good time to reconsider that position.
> They still aren't changing it crazily frequently, but I now run an 
> OpenVPN server at home and it is a bit inconvenient when they change my 
> home IP and I don't notice before going on a business trip or something.
> I'd like to set up an alert that lets me know when my external IP 
> address has changed.
> The box that is in a position to notice that the IP address has changed 
> is on the outer edge of my network connected directly to the internet. 
> It runs LFS.
> Deeper inside my network, accessible from the LFS box via the VPN, is a 
> Debian Stretch machine where I do most of my work.
> I've created a very simple script that is capable of parsing the output 
> of "ip addr" and comparing the returned ip address for the relevant 
> interface to a stored ip address, and thus being able to tell if the IP 
> address has changed. What I'd like to do now is make a means for the LFS 
> box to be able to notify me of the fact that the external-facing IP 
> address has changed. 
> My Debian machine runs exim4 and has a reasonably basic setup that 
> allows it to accept mails from other machines on the network (although I 
> may need to fiddle around with getting mail to come through the VPN) and 
> deliver it either locally or using a friendly mail provider as a 
> smarthost. I've successfully sent and received mail between this machine 
> and a Buster machine on the same network, those two machines can see 
> each other without the VPN. The Buster machine was also running exim4.
> The LFS machine is, by design, very sparsely configured with only 
> software I truly needed installed. I am willing to add software but wish 
> to minimise the risk of installing something that opens up 
> external-facing vulnerabilities as much as possible. What I'd really 
> like is a piece of software that can reach out to my Stretch machine 
> through the VPN to present an email for delivery without offering a 
> local MTA that, improperly configured, might end up listening to the 
> outside world and thus present a security risk.
> I've looked at sendmail, postfix and of course exim4, and these are MTAs 
> which could certainly do the job but which also present the risk of 
> listening to the internet, especially if I do something stupid in the 
> configuration which is entirely feasible. And from some basic tests I 
> did on my Stretch machine I think the mail command expects there to be a 
> local MTA for it to talk to...
> My image of an ideal solution is a piece of software that can present 
> email to a remote MTA (ie an MTA not on the local machine) for delivery, 
> but is not itself an MTA, and certainly has no capability to listen for 
> incoming mail.
> Thanks in advance
> Mark