On Mon, 8 Apr 2019 21:33:03 +0900 Mark Fletcher <mark2...@gmail.com> wrote:
> > 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. > a) Sendmail. Not the full-featured MTA, but the utility. https://clients.javapipe.com/knowledgebase/132/How-to-Test-Sendmail-From-Command-Line-on-Linux.html b) Write it yourself. If you can do simple scripting then you can write something that talks basic SMTP to a remote SMTP server. Here's basic unencrypted SMTP: https://my.esecuredata.com/index.php?/knowledgebase/article/112/test-your-smtp-mail-server-via-telnet There are many similar sites, some going into more detail including how to find out the recipient's MX server if you don't know already. https://www.port25.com/how-to-check-an-smtp-connection-with-a-manual-telnet-session-2/ Other sites explain how to use authenticated SMTP and TLS. If you later get a fixed IP address and want to run your own mail server, you can test it for relaying using the telnet technique. Or rely on numerous websites... c) Use a standard MTA and tell it not to listen to anything from outside your network. Use your firewall to not accept SMTP on the WAN port, and unless you have previously received email directly then the SMTP port shouldn't be open anyway. Use the MTA's configuration to listen only to localhost. Restart it and check where it's listening with netstat -tpan as root. That way you have two mechanisms to prevent access, even if you misconfigure one of them you should still be OK. After you have the MTA running and sending email where you want it to go, use ShieldsUp!! on https://grc.com to check which ports are open to the outside. Select 'All Service Ports' to check TCP/1-1055. -- Joe
