For some years now, I’ve been running all my outgoing mail through localhost and delivering directly from exim4. It works really well from everywhere but home. Well, it used to work, but at some point my ISP apparently decided they don’t want to be blacklisted. or something. Anyway, they apparently blocked outgoing SMTP to anywhere but their own relays. Not that they notified their customer support about it, of course.
At that time I had another machine running PPPoE, firewall and a web broser. I configured exim to use a smarthost on that machine and set up firewall rules to route all outgoing port 25 connections to the local server. It was somewhat slower but it worked. Case closed.

Enter 2006 and DigiTV. With that, I had to move to the contemporary way of running NAT on the modem/router/AP. Of course, my ingeniously complicated SMTP set-up was out of the loop. Every now and then there would be an e-mail laying in my machine for 20 hours or so… Not really instant feedback or what?

As usual, one has just to google for the right keywords to solve any and all problems. I suppose I hadn’t queried for “exim fallback smarthost” until this morning.

My problem was solved by changing the remote_smtp transport to:

remote_smtp:
debug_print = "T: remote_smtp for $local_part@$domain"
driver = smtp
fallback_hosts = zen.estpak.ee:mail.neti.ee

I’m lucky to only have one network that limits this. For any other nets, I suppose new hosts can be added and exim can be left to try them out one-by one.