Managed location
The aspect of mobile computing that I left out was software: the system software which manages network connections should be able to manage this as well. Could DHCP, the protocol which assigns your machine an IP address when it connects to the network, send an SMTP server address along with the other addresses it sends? How about if the system includes a “location manager” daemon which silently selects the appropriate SMTP server from an established list, based on the network you’ve just joined? (Even better if that location manager has a little bit of a brain, and can identify the scope of a particular server—for example, it might set my server to smtp.comcast.com on any network served by Comcast, not just my home network.)
The point is, this is exactly the sort of adjustment which can be managed with logical rules, which means it’s perfect for software. Why is the machine nagging me about it?
Now Playing: I Wish You Would from Drops of Jupiter by Train