Agent is the Usenet client from Forté; I have used it for about a decade or so. According to their FAQ, individual newsgroup database files up to 8 GB are supported.
Since each file represents a single newsgroup, and I subscribe to 31 newsgroups, I might interpret this as allowing 248 GB worth of articles and binaries and whatnot. Not a good idea if you have, say, a 250-GB drive. (Really not a good idea if you have less than that.)
Anyway, I cleared out 9 GB last night just shy of 696,000 individual items and it took almost an hour. I don’t think I should let the stuff go for so long next time.