Exim

Configure Exim to relay outgoing mail through the gateway as a smart host, using a manualroute router with authenticated SMTP transport.

1. Add a router (typically in /etc/exim4/conf.d/router/ or your distribution's equivalent) that sends outgoing mail to the gateway's inbound server as a smart host:

   send_via_gateway:
     driver = manualroute
     domains = ! +local_domains
     transport = gateway_smtp
     route_list = "* smtp.adlerwacht.com::587"

1. Add a matching authenticated transport:

   gateway_smtp:
     driver = smtp
     hosts_require_auth = smtp.adlerwacht.com
     hosts_require_tls = smtp.adlerwacht.com

1. Add your gateway account's credentials to Exim's authenticator configuration (typically passwd.client or your distribution's equivalent):

   smtp.adlerwacht.com:you@yourcompany.com:your-mailbox-password

1. Validate the configuration and restart Exim:

   exim -bV
   systemctl restart exim4

1. Send a test message from the server to confirm it now routes through the gateway.