I have queue_domains or queue_smtp_domains set, and use -qf to force delivery of waiting mail when I dial in. How can I arrange for any new messages that arrive while I'm connected to be delivered immediately?

Instead of queue_domains or queue_smtp_domains, use the queue_only_file option. This causes messages to be queued if a particular file exists. If you put the word smtp > before the file name, the queueing applies only to domains that are

delivered by SMTP, thus not affecting local deliveries:

queue_only_file = smtp/etc/present/when/not/connected

Then, in the scripts which are run when you connect and disconnect, arrange to remove the file after connection, and create it just before disconnection.