Ah haaa... the former moderator of BATPOWER_UK puts in an appearance...
Ah! Too true! Never got beyond batch file programming on the PC. That's why I just do the documentation these days!
(Better explain to Carol, BATPOWER_UK was FidoNet echomail. FidoNet was an amateur version of the internet from the days before the public had access. Echomail is the equivalent of Usenet/Newsgroups. None of it was anything to do with "The Bat".)
Is nPop one of the ones that leaves the mail on the server,
Like most programs you have the choice. The defaults leave it on the server and only downloads the first 100 lines of each message, but you can change everything. Some people just use it as a mail notifier (downloading no message content at all) as it uses so little resources. Downloading a limited number of lines means that you can leave giant attachments behind and still read the message, are pretty well immune from viruses carried in the HTML part of mail, etc etc.
and you have to deliberately specify particular messages to be saved to disk, as opposed to something like TheBat! which saves everything in a database?
There's no database (messagebase to the FidoNetters amongst us!). Messages for each account are saved in a file as plain text (if you want to!). Makes it beautifully easy to interrogate old mail, even if you give up the program.