Using sendmail over SSH

Question

I have a SSH access to the server with working sendmail provided by my hoster. I want to configure my local sendmail to use remote server as a relay. How can I do that? Is it posiible at all?

Note: I can write script to run something like ssh user@host sendmail ... but it seems to me like there is a better solution.

Answer 1

Prepare SSH

Locally, create a new SSH key without password. In these examples, it will be located at /etc/mail/ssh-sendmail-key and owned by the MAILUSER user. Change MAILUSER to whatever Unix account your local system uses: postfix, sendmail, mail, ... Using root or nobody is not recommended.

# ssh-keygen -f /etc/mail/ssh-sendmail-key -N ""
# chown MAILUSER /etc/mail/ssh-sendmail-key{,.pub}

Append the contents of /etc/mail/ssh-sendmail-key.pub to the server's authorized_keys file:

ssh-rsa AAAA....

Postfix

Create a ssh transport in master.cf:

ssh    unix    -       n       n       -       -       pipe
    user=MAILUSER argv=/usr/bin/ssh -i /etc/mail/ssh-sendmail-key myhostserver /usr/sbin/sendmail -i $recipient

In main.cf, add:

default_transport = ssh

Exim

Router:

ssh:
    driver = manualroute
    domains = ! +local_domains
    transport = ssh
    route_list = * foo

Transport:

ssh:
    driver = pipe
    user = MAILUSER
    command = /usr/bin/ssh -i /etc/mail/ssh-sendmail-key myhostserver /usr/sbin/sendmail -i $RECIPIENT